CBSE Class 10 Science Carbon and its Compounds VBQs

MULTIPLE CHOICE QUESTIONS

Question. The electronic configuration of an element is found to be 2, 4. How many bonds can one carbon atom form in a compound?
(a) 1
(b) 2
(c) 4
(d) 6
Answer. C

Question. Carbon forms four covalent bonds by sharing its four valance electrons with four univalent atoms, e.g hydrogen. After the formation of four bonds, carbon attains the electronic configuration of
(a) helium
(b) neon
(c) argon
(d) krypton
Answer. B

Question. The image represents the structure of a few hydrocarbon compounds.

Which of these compounds can be classified as alkynes?
(a) only (A)
(b) only (B)
(c) both (A) and (D)
(d) both (B) and (C)
Answer. C

Question.4. The image represents a chemical reaction where ethanol is oxidized using potassium dichromate and sulphuric acid.

Which option represents the product “X”?
(a) CH₂O
(b) CH₃OH
(c) CH₃H₂O
(d) CH₃COOH
Answer. D

Question. The image represents the structure of a carbon compound known as ethane.

Which option explains the naming of ethane?
(a) the presence of functional group connected with a single bond
(b) as it contains two carbon atoms and a single bond connects the carbon atoms
(c) carbon compound with a total number of eight atoms are named as ethane
(d) as it contains six hydrogen atoms and a single bond connects the carbon and hydrogen atom
Answer. C

Question. The image represents a carbon compound.

Which functional group is present in the compound?
(a) alcohol
(b) aldehyde
(c) carboxylic acid
(d) ketone
Answer. D

Question. A carbon compound contains two atoms of carbon. Which name should the carbon compound bear?
(a) Butane
(b) Ethane
(c) Methane
(d) Propane
Answer. B

Question. The chemical reaction shows the addition of chlorine gas to hydrocarbon in the presence of sunlight.
CHCl₃ + Cl₂ → CCl₄ + HCl
How does chlorine react to a hydrocarbon compound in the presence of sunlight?
(a) it adds hydrogen into the compound
(b) it adds an oxygen atom into the compound
(c) it substitutes hydrogen atom from the compound
(d) it breaks double and triple bonds into a single bond
Answer. C

Question. Methane, ethane and propane are said to form a homologous series because all are-
(a) Hydrocarbons
(b) saturated compounds
(c) aliphatic compounds
(d) differ from each other by a CH₂ group
Answer. D

Question. Which of the following belongs to a homologous series of alkynes?
C₆H₆, C₂H₆, C₂H₄, C3H₄
(a) C₆H₆
(b) C₂H₆
(c) C₂H₄
(d) C₃H₄
Answer. D

Question. The gas evolved when ethanol reacts with sodium metal is
(a) H₂
(b) CO₂
(c) H₂O
(d) CO
Answer. A

Question. While cooking ,if bottom of the vessel is getting blackened on the outside, it means that
(a) The food is not cooked properly
(b) The fuel is not burning properly
(c) The fuel is wet
(d) The fuel is burning completely
Answer. B

Question. When ethanoic acid reacts with ethanol a sweet smelling product is formed . The functional group present in the product is
(a) Aldehyde
(b) Ketone
(c) Alcohol
(d) Ester
Answer. D

Question. Glacial acetic acid is a
(a) Frozen acetic acid
(b) 5-8% of solution of acetic acid in water
(c) Mixture of acetic acid and alcohol
(d) None of these
Answer. B

Question. Which of the following is incorrectly matched?
(a) Vinegar → carboxylic acid
(b) C2H6 → alkane
(c) Ethanol → alcohol
(d) Methanol → ketone
Answer. D

Question. The number of structural isomers for alkane with a molecular weight 72 is
(a) 2
(b) 3
(c) 4
(d) 5
Answer. B

Question. The carbon exist in the atmosphere in the form of
(a) Carbon monoxide only
(b) Carbon monoxide in traces and carbon dioxide
(c) carbon dioxide only
(d) coal
Answer. B

Question. The property of carbon atom by virtue of which it forms bond with other carbon atom is called
(a) chemical bonding
(b) polymerization
(c) catenation
(d) carbonization
Answer. C

Question. Oils on treating with hydrogen in the presence of palladium or nickel catalyst forms fats. This is an example of
(a) addition reaction
(b) substitution reaction
(c) displacement reaction
(d) oxidation reaction
Answer. A

Question. The hetero atoms present in CH_3-CH₂-O-CH₂-CH₂-Cl are
(i) oxygen           (ii) carbon
(iii ) hydrogen    (iv) chlorine
(a) (i) and (ii)
(b) (ii) and (iii)
(c)(iii) and (iv)
(d) (i) and (iv)
Answer. D

ASSERTION AND REASON QUESTIONS:

DIRECTION: Each of these questions contains an Assertion followed by Reason. Read them carefully and answer the question on the basis of following options. You have to select the one that best describes the two statements.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Question. Assertion(A) : Carbon is the only element that can form large number of compounds.
Reason (R) : Carbon is tetravalent and shows the property of catenation.
Answer. D

Question.Assertion(A) : If the first member of a homologous series is methanal, its third member will be propanal.
Reason (R) : All the members of a homologous series show similar chemical properties.
Answer. B

Question. Assertion(A) : Diamond and graphite are allotropes of carbon.
Reason (R) : Some elements can have several different structural forms while in the same physical state. These forms are called allotropes.
Answer. A

Question. Assertion(A) : Soaps are not suitable for washing purpose when water is hard.
Reason (R) : Soaps have relatively weak cleansing action.
Answer. B

Question. Assertion(A) : Carbon compounds can form chain, branched and ring structures.
Reason (R) : Carbon exhibits the property of catenation.
Answer. A

Question. Assertion (A) : Carbon monoxide is extremely poisonous in nature.
Reason (R) : Carbon monoxide is formed by complete combustion of carbon.
Answer. C

CASE-STUDY BASED QUESTIONS.

Read the passage and answer the following questions.

2. As the reaction takes place, a sweet fruity smell can be sensed coming out from the test tube.

a) What can be the reason behind the fruity smell?
Answer : Ester formation

b) What are the reactants of the reaction mixture? Write the chemical reaction involved.
Answer : Reaction mixture: Ethanol (Alcohol) + Acetic Acid (Carboxylic Acid) , Reaction: Esterification

c) Why is it advised to heat the test-tube in a water bath and not directly?
Answer : As Alcohol being one of the reactants and its highly flammable, it should not be heated directly. Hence heated in a water bath.

Very Short Answer Type Questions

Question. An organic compound burns with a sooty flame. Is it a saturated or an unsaturated compound?
Answer: It is an unsaturated compound. Unsaturated compounds have more percentage of carbon as compared to saturated compounds. Thus, unsaturated compounds undergo incomplete combustion in the presence of air producing a yellow flame with lots of black smoke.

Question. Why carbon does not form the ionic compounds?
Answer: For formation of ionic compounds, carbon should either gain four electrons to form C₄^– ions or should lose four electrons to form C₄⁺ ions but formation of both these ions is not possible due to high energy considerations.

Question. Write the molecular formula of the 2^nd and 3^rd member of the homologous series whose first member is methane.
Answer: Methane, CH₄ is an alkane. Alkanes have general formula, C_nH_{2n + 2}. 2nd member of homologous series of alkanes is C2H6 i.e., ethane.
3rd member of homologous series of alkanes is C₃H₈ i.e., propane.

Question. Select saturated hydrocarbons from the following : C₃H₆; C₅H₁₀; C₄H₁₀; C₆H₁₄; C₂H₄
Answer: Saturated hydrocarbons have general formula, C_nH_2n+2. Among the given compounds only C₄H₁₀ and C₆H₁₄ satisfy the above formula. Thus, these are saturated hydrocarbons.

Question. Write the name and formula of the 2nd member of homologous series having general formula CnH2n – 2. 
Answer: General formula, C_nH_{2n + 2} belongs to alkyne series. The second member of this series is propyne i.e., (C₃H₄) or CH₃ — C ≡ CH.

Question. LPG (liquefied petroleum gas) is used as a fuel for cooking in homes. Why is LPG stored as a liquid?
Answer: LPG is stored as a liquid so that more fuel can be kept in a container. Liquids contain more particles per unit volume than gases. It is also easier to transport liquids than gases.

Question. Give different forms in which carbon occurs in nature.
Answer: Carbon occurs in free form e.g., graphite and diamond, in combined form like carbon dioxide, carbonates, etc. In earth’s crust – 0.02% and in atmosphere – 0.03%.

Question. Write the molecular formula of first two members of homologous series having functional group —Cl.
Answer: The molecular formula of first two members of homologous series having –Cl functional group are CH₃Cl and CH₃CH₂Cl.

Question. Give the electron dot structures for (a) CCl₄ and (b) C₂H₂.
Answer: (a) : Carbon has 4 valence electrons and chlorine has 7 valence electrons. 

Question. What are covalent compounds?
Answer: A covalent compound is a molecule formed by covalent bonds, in which the atoms share one or more pairs of valence electrons.

Question. What are the two properties of carbon which led to the huge number of carbon compounds we see around us? Define them.
Answer : a) Catenation- Property to bond with itself on a large scale
b) Tetravalency- property to make 4 covalent bonds

Question. Is the given statement true? If not, rewrite the correct statement. 'Diamond and graphite are the covalent compounds of carbon elements.
Answer : No. 'Diamond and graphite are allotropes of carbon.

Question. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Answer : Bromine water test: Alkenes are unsaturated and decolourise an orange solution of bromine water. Alkanes are saturated and do not react with bromine water, so the orange colour persists 

Question. Match the reaction given in column A with the names given in column B

Answer : a- iv, b- i, c- ii, d- iii

Short Answer Type Questions

Question. A hydrocarbon molecule has 3 carbon atoms. Write down its molecular formula if it is an : (i) alkane (ii) alkene (iii) alkyne.
Answer: The number of carbon atoms in the molecule of this hydrocarbon is 3, that is, n = 3.
(i) The general formula of an alkane is C_nH_2n+2. On putting n = 3, we get C₃H₂×3+2 or C₃H₈ (propane).
(ii) For alkene having general formula C_nH_2n, we get, C₃H₂ × 3 or C₃H₆ (propene).
(iii) For alkyne having general formula C_nH_2n–2 we get C₃H₂ × 3 – 2 or C₃H₄ (propyne).

Question. ‘Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame’’. Why?
Answer: An unsaturated hydrocarbon has high concentration of carbon, which does not get oxidised by the atmospheric oxygen. Thus, unburnt carbon appears in the form of soot and hence the flame is sooty.

Question. (a) What would be observed on adding a 50% solution of alkaline potassium permanganate drop by drop to some warm ethanol taken in a test tube?
(b) Write the name of the compound formed during the chemical reaction.
Answer: (a) The pink colour of potassium permanganate would be discharged.
(b) Ethanoic acid.

Question. Samir took ghee in a beaker and heated it. Ghee readily melts and easily boils too, but when he tries to pass electricity through ghee, it does not conduct electricity. Give reason for his observation.
Answer: Ghee is a saturated hydrocarbon or we can say that it is a carbon compound with covalent bond. Covalently bonded molecules are seen to have strong bonds within the molecule, but inter-molecular forces are small. This gives rise to the low melting and boiling points of these compounds.
Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductor of electricity, that is why ghee did not conduct electricity.

Question. What happens when wood is burnt in a limited supply of oxygen? Name the residue left behind after the reaction and state two advantages of using this residue as a fuel over wood.
Answer: When wood is burnt in a limited supply of oxygen, destructive distillation takes place with the formation of wood charcoal.
The residue left after the reaction is wood charcoal.
Advantages of using wood charcoal over wood:
(a) Wood charcoal burns without smoke.
(b) It does not liberate any poisonous gases on burning.

Question. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.
Answer: Carbon exhibits catenation much more than silicon or any other element due to its smaller size which makes the C–C bonds strong while the Si–Si bonds are comparatively weaker due to the large size of the atoms.

Question. Write the next higher homologue of the following : (i) C₃H₆ (ii) C₅H₈
Answer: (i) C₄H₈ (ii) C₆H₁₀

Question. The number of carbon compounds is more than those formed by all other elements put together. Justify the statement by giving two reasons.
Answer: The following reasons are :
(i) Due to self-linking ability of carbon which is known as catenation.
(ii) Since carbon has valency of four it can form with four other atoms of carbon or atoms of some other monovalent element.
(iii) Due to small size of carbon it forms very strong or stable bonds with other elements.

Question. What is a homologous series? Which two of the following organic compounds belong to the same homologous series?
C₂H₆, C₂H₆O, C₂H₆O₂, CH₄O
Answer: A group of members of the same class of organic compounds, which differ from each other by a – CH₂ group, when arranged in the ascending order of molecular mass is called a homologous series.
CH₄O and C₂H₆O are homologues since they differ by a – CH₂ group.

Question. (a) How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?
Answer : Ethanol does not react with sodium carbonate. However, carboxylic acid reacts with sodium carbonate with the liberation of carbon dioxide gas which turns limewater milky.
(b) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?
Answer: Carbon dioxide gas.
The gas when passed through limewater turns the limewater milky.

Question. What is a functional group in a carbon compound. Identify the functional group present in CH₃COOH and C₂H₅OH.
Answer: An atom or a group of atoms which gives the same characteristic properties to a compound is called a functional group.
Functional group in : CH₃COOH — Carboxylic acid group C₂H₅OH — Alcoholic group

Question. What is meant by functional group in an organic compound? Name the functional group present in :
(a) CH₃CH₂OH (b) CH₃COOH
Answer: Functional group is an atom or group of atoms or reactive part of compound which determines chemical properties of compounds.
(a) —OH (Alcohol) (b) —COOH (Carboxylic acid)

Question. (a) What is a ‘homologous series’ of substances?
(b) In an organic compound, which parts largely determine its physical and chemical properties?
Answer: (a) A group or series of organic compounds having the same general formula and similar graded physical and chemical properties is called a homologous series.
(b) The functional group of an organic compound determines its physical and chemical properties.

Question. (a) Give a chemical test to distinguish between ethanol and ethanoic acid.
(b) Name the product formed when an organic acid reacts with an alcohol in the presence
of an acid catalyst. What is the name assigned to this type of reaction.
Answer: (a) Ethanoic acid liberates carbon dioxide gas on reacting with sodium carbonate or sodium hydrogen carbonate. Ethanol gives no such reaction with sodium carbonate or sodium hydrogen carbonate.
(b) Ester
Esterification

Question. Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer: Bond formation in CH₃Cl

Carbon forms single covalent bond by sharing one electron pair with three hydrogen atoms and one chlorine atom. Chlorine being more electronegative adds polar nature to C—Cl bond.

Question. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer: Soap molecules have two ends with different properties. One end is hydrophilic, which dissolves in water and other end is hydrophobic, it dissolves in hydrocarbons. When  soap is added to water, the ionic end of soap will form a unique orientation and keep the hydrocarbon tail away from it.
The cluster of molecules is formed in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. Hence, micelle formation takes place.
Soap is soluble in ethanol hence the micelle formation will not take place.

Question. Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer: Butter is saturated compound and oil is unsaturated compound. Test
alk. potassium permanganate + Unsaturated → Pink colour disappear.
(Pink colour) hydrocarbon
Therefore, when we add oil to a test tube containing alkaline potassium permanganate solution, the pink colour of the solution disappear. Colour of alkaline potassium permanganate will not disappear in the test tube containing butter.

Question. Why are carbon and its compounds used as fuels for most applications?
Answer: Carbon and its compounds undergo combustion to produce heat, the amount of heat released can be handled and used so they are used as fuels for most applications.

Question. What is an homologous series? Explain with an example.
Answer: It is a group of members of same class of organic compound having similar chemical properties, they have same general formula.
They have same functional group, when arranged in the ascending order of molecular mass they differ by 14 a.m.u. or —CH₂ group.
Example: Alkane General formula — CnH_2n+2

Question. Explain the formation of scum when hard water is treated with soap.
Answer: Hard water contains salts of calcium and magnesium. When soap molecule comes in contact with these salts it forms a curdy white precipitate (compound insoluble in water) called scum.
                        Soap + Hard water ⎯→ scum

Question. What change will you observe if you test soap with litmus paper (red and blue)?
Answer: Soap is alkaline in nature, hence it will turn red litmus into blue, blue litmus will remain blue.

Question. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer: Physical Properties

Question. What is hydrogenation? What is its industrial application?
Answer: When unsaturated hydrocarbons (double/triple bond) are reacted with hydrogen in presence of a catalyst like nickel, the hydrogen gets added across the double/triple bond and converts the unsaturated hydrocarbon into saturated hydrocarbon. Such reaction is called addition reaction or hydrogenation .

Question. Draw the electron dot structure for
(a) ethanoic acid.
(b) H₂S.
(c) propanone.
(d) F₂.
Answer: The electron dot structure are as follows:
(a) Ethanoic acid – CH₃COOH

Question. Explain the mechanism of cleaning action of soaps.
Answer: Soap molecule has two ends, the charged end that gets attracted towards water is called hydrophilic and the long carbon chain that repels water is called hydrophobic end. When soap is dissolved in water, the carbon chain i.e., hydrophobic end gets attracted towards the oil, dirt and grease. The hydrophilic end stays away from this.
The micelle formation takes place.
The tail entangles dirt, oil or grease, if required the agitation is done. Lot of rinsing is a done with water so that water molecules attract charged (Na+) end and carries the soap molecules with dirt attached to it and clean the clothes, utensils, etc.

Question. Which of the following hydrocarbons undergo addition reactions?
C₂H₆, C₃H₈, C3H6, C₂H₂ and CH₄.
Answer : Addition reaction takes place in unsaturated hydrocarbons.
Hence C₃H₆ and C₂H₂ are unsaturated hydrocarbons and will show addition reaction.

Question. State two properties of carbon which lead to a very large number of carbon compounds.
Answer: Carbon forms a large number of carbon compounds like long chains which may be straight or branched chains or ring of different sizes due to its tetravalency and unique property of catenation. Carbon due to its small size forms exceptionally stable compounds by forming strong bonds.

Question. An allotrope of carbon has a molecular mass of 720. Discuss its structure.
Answer: Atomic mass of C = 12 and molecular mass of an allotrope of carbon 720. 
∴ No. of C atoms = 720/12 = 60.
Thus, the allotrope of carbon is C60, i.e., Buckminster fullerene and its structure is similar to a soccer ball.

Question. The molecular formulae of alkenes X and Y are CxH₈ and C₁₀Hy respectively. What are the relative molecular masses of X and Y?
Answer: The general formula of an alkene is C_nH_2n.
Thus, the molecular formula of X is C₄H₈, and the molecular formula of Y is C₁₀H₂₀.
Molecular mass of X = (4 × 12) + (8 × 1) = 56
Molecular mass of Y = (10 × 12) + (20 × 1) = 140

Question. (i) Which allotrope of carbon is used for making cores of lead pencils?
(ii) Which allotrope of carbon is used for making expensive jewellery?
(iii) Name an allotrope of carbon which contains both single and double bonds.
Answer: (i) Graphite
(ii) Diamond
(iii) Graphite

Question. (a) What is a homologous series of compounds? List any two of its characteristics.
Answer: (a) A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent) members of the series are differ by a CH₂ unit or 14 mass units. Two characteristics of homologous series are :
(i) The successive compounds of the homologous series differ by —CH₂ unit i.e. 14 mass units.
(ii) Each homologous series belongs to similar class of compounds which shows the same properties.
(b) Next higher homologue of C₃H₇OH is C₄H₉OH i.e., butanol.

Question. Write the molecular formula of the following compounds and draw their electron-dot structures:
(i) Ethane (ii) Ethene (iii) Ethyne
Answer: (i) Molecular formula of ethane is C₂H₆. Its electron dot structure is :
(ii) Molecular formula of ethene is C₂H₄. Its electron dot structure is :
(iii) Molecular formula of ethyne is C₂H₂. Its electron dot structure is :

Long Answer Type Questions

Question. An organic compound ‘A’ is widely used as a preservative in pickles and has a molecular formula C₂H₄O₂. This compound reacts with ethanol to form a sweet smelling compound ‘B’.
(a) Identify the compound ‘A’.
(b) Write the chemical equation for its reaction with ethanol to form compound ‘B’.
(c) How can we get compound ‘A’ and ‘B’?
(d) Which gas is obtained when compound ‘A’ reacts with washing soda? Give the equation.
(e) Write an equation to obtain ‘A’ back from ‘B’.
Answer: (a) ‘A’ is CH₃COOH acetic acid.
(b) CH₃COOH + C₂H₅OH ⎯⎯→ CH₃COOC₂H₅ + H₂O
(c) We can get compound A back by the process of saponification.
(d) A + washing soda ⎯⎯→ CO₂ gas is produced
2CH₃COOH + Na₂CO₃ ⎯⎯→ 2CH₃COONa + H₂O + CO₂
(e) Saponification

Question. (a) What is homologous series of compounds? List any two characteristics of a homologous series.
(b) (i) What would be observed on adding 5% solution of alkaline potassium permanganate solution drop by drop to some warm ethanol taken in a test tube?
(ii) Write the name of the compound formed during the chemical reaction.
(c) How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property? 
Answer: (a) Organic compounds when arranged in series having same general formula and similar chemical properties is called homologous series.
Two characteristics of homologous series.
(i) Each successive member differ by —CH₂ group, 14 u.
(ii) The method of preparation and chemical properties of members of homologous series is same.
(b) (i) The colour of KMnO₄ will get discharged because ethanol gets oxidised to form ethanoic acid.

Question. (a) Why two carbon atoms cannot be linked by more than three covalent bonds.
(b) Explain the following :
(i) Diamond is a covalent solid, yet has high melting point.
(ii) Graphite is a good conductor of electricity but diamond is not.
(iii) Diamond is used for making tools for cutting and drilling.
Answer: (a) Since the maximum angle strain is obtained when the two carbon atoms are linked by three covalent bonds, therefore, two carbon atoms cannot be linked to each other by more than three covalent bonds.
(b) (i) It is a giant molecule containing a large number of carbon-carbon single covalent bonds. To break these covalent bonds, a large amount of energy is needed and hence diamond has a high melting point.
(ii) Graphite has two-dimensional layered structure containing fused hexagonal rings of carbon atoms. Only three valence electrons are used for bond formation while the fourth electron is free to move. Due to ability of this free electron to move, graphite is a good conductor of heat and electricity. Since in diamond, all the four electrons are involved in bond formation, therefore, diamond is a bad conductor of electricity.
(iii) Diamond is a good conductor of heat and is used for making cutting and drilling tools because the heat generated during cutting and drilling is easily absorbed by the network
structure without overheating the diamond tool.

Question. The compounds, methanal, ethanal, propanal and butanal belong to the homologous series, called aldehydes. The table shows some information on these four aldehydes. 36
(a) List two characteristics of this homologous series using the information shown in the table.
(b) Compare the molecular formulae of the four aldehydes listed in the table. What conclusion can you make?
(c) Draw the electronic structure of ethanal. You need to show only the outer shell electrons.
Answer: (a) They have the same functional group, CHO group. 
There is a gradual change in their physical properties. Boiling points of aldehydes increase and their solubility in water decreases as their molecular sizes increase.
(b) Comparing the molecular formulae:
Conclusion : Each member of the series differs from the next by a - CH₂ unit.

Question. (a) Define the term ‘isomers’.
(b) Draw two possible isomers of the compound with molecular formula C₃H₆O and write their names.
(c) Give the electron dot structures of the above two compounds.
Answer: (a) Isomers are those molecules which have the same molecular formula but different structural formula i.e., show different properties.
The structures of possible isomers of butane (C₄H₁₀) are :
The first three members of alkane series are :
(i) CH₄ (methane)
(ii) C₂H₆ (ethane)
(iii) C₃H₈ (propane)
In the above members of alkane series, it is not possible to have different arrangements of carbon atoms. Thus, we cannot have isomers of first three members of alkane series.
(b) Two possible isomers of the compound, C₃H₆O are :
(c) The electron dot structures of propanone and propanal are :

Question. The table given below shows some information about four organic compounds P, Q, R and S.
(a) (i) Which homologous series does C₃H₈ belong to?
(ii) Why are P, Q, R and S classified as hydrocarbons?
(b) Which of these organic compounds belong to the alkane series?
(c) Based on the information given above, state one characteristic of the alkane series.
Answer: (a) (i) As C₃H₈ has general formula C_nH_2n+2 thus it belongs to alkane.
(ii) P, Q, R and S are classified as hydrocarbons because these compounds are made up of carbon and hydrogen only.
(b) C₃H₈, C₄H₁₀ and C₅H₁₂ all have general formula C_nH_2n+2 thus, all of these belong to alkanes.
(c) They have general formula CnH_2n+2 and their melting points and boiling points increase with increase in molecular mass.

Question. (a) State the reason why carbon can neither form C₄⁺ cations nor C₄^– anions, but forms covalent bonds. Also state reasons to explain why covalent compounds
(i) are bad conductors of electricity
(ii) have low melting and boiling points.
(b) Write the structural formula of benzene, C₆H₆.
Answer: (a) Ionic compounds are formed either by gaining or losing electrons from the outermost shells, but carbon which has four electrons in its outermost shell cannot form ionic
bonds because
– If carbon forms ionic bonds by gaining four electrons to attain a noble gas configuration then it would be difficult for six protons in the nucleus to hold ten electrons.
– If carbon forms ionic bonds by loss of four electrons then it would require a lot of energy to remove these electrons from outermost shell.
Due to these reasons carbon forms covalent bonds by sharing the valence electrons.
(i) Covalent compounds are generally poor conductors of electricity because they do not have free electrons or ions.
(ii) Covalent compounds have low melting and boiling points because the forces of attraction between molecules of covalent compounds are very weak. On applying a small amount of heat these molecular forces break.

Case Based Questions :

Read the passage given below and answer the following When an element exists in two or more different forms in the same physical state, these different forms are called allotropes and the phenomenon is known as allotropy. Allotropes have similar chemical properties but they differ in their physical properties. Carbon exists in crystalline and amorphous forms. In crystalline form, it occurs as diamond, graphite and fullerenes. Diamond is a colourless, transparent substance having extraordinary brilliance. It is the hardest natural substance known. It is used for cutting marble, granite and glass. Graphite is a greyishblack, opaque substance. It is lighter than diamond i.e., it has lower density. It has sheet like structure having hexagonal layers. One layer slides over the other layer which makes it soft to touch. It is the reason that graphite is used as a lubricant.

Question. Which three allotropes of carbon, do the given figures represent? 

         (I)           (II)         (III)
(a) Diamond Graphite Buckminster fullerene
(b) Graphite Buckminster Diamond fullerene
(c) Diamond Buckminster Graphite fullerene
(d) Graphite Diamond Buckminster fullerene

Answer : D

Question. Which of the following is correct about the structure of diamond?
(a) Carbon atoms are held together by single covalent bonds.
(b) Electrons move freely through the structure.
(c) Layers of atoms slide easily over each other.
(d) Carbon atoms conduct electricity in the molten state.

Answer : A

Question. Structures of two different forms of carbon are given below : 

Identify the two forms (I and II respectively) and how are they related to each other?
(a) Diamond, Graphite, Isotopes of carbon
(b) Graphite, Diamond, Allotropes of carbon
(c) C₁₂, C₁₄, Allotropes of carbon
(d) C₁₄, C₁₂, Isotopes of carbon

Answer : B

Question. Identify the incorrect statement(s).
(I) Diamond is the hardest substance known while graphite is smooth and slippery.
(II) Diamond is made up of billions of carbon atoms. Each carbon atom is bonded to four other carbon atoms in a tetrahedral manner to form a giant lattice. All carbon atoms are bonded by strong covalent bonds.
(III) Graphite is a poor conductor of electricity unlike other non-metals.
(IV) Graphite has a giant covalent structure that is made up of layers of carbon atoms. In each layer, each carbon atom is bonded to three other carbon atoms to form hexagonal rings of carbon atoms.
(a) (I) and (III)
(b) Only (III)
(c) (II) and (IV)
(d) (I), (II) and (IV)

Answer : B

Question. Substance X is a moderate conductor of electricity. Substance X has the structure shown below : 
Which statements about substance X are correct?
(I) It is a covalent compound.
(II) It has a giant molecular structure.
(III)It has the same structure as graphite.
(IV) It has the same structure as diamond.
(a) (I) and (III)
(b) (II) and (III)
(c) (II) and (IV)
(d) (I), (II) and (IV)

Answer : C

Read the passage given below and answer the following questions from 36 to 40. Two allotropic forms of carbon which are crystalline in nature, are diamond and graphite. They differ physically but chemically they are similar. Diamond is the hardest crystalline form of carbon. In diamond, each carbon atom is linked to four other carbon atoms by covalent bonds. In graphite, each carbon atom is linked to three other carbon atoms by covalent bond. Graphite is relatively soft and greasy. It is also a good conductor of electricity. The C — C bond length in graphite is 141.5 pm while in diamond it is 154 pm.

Question. Which of the following types of binding forces is present in the structure of diamond?
(a) Ionic
(b) van der Waals’
(c) Covalent
(d) None of these

Answer : C

Question. Diamond is not a good conductor of electricity because
(a) it is very hard
(b) its structure is very compact
(c) it is not water soluble
(d) it has no free electron.

Answer : D

Question. Which of the following is a good conductor of heat and electricity?
(a) Coal
(b) Diamond
(c) Charcoal
(d) Graphite

Answer : D

Question. Graphite is a good conductor of electricity because
(a) it has free electrons
(b) it has free atoms
(c) it is crystalline
(d) it is soft and greasy.

Answer : A

Question. Which of the following is the structure of diamond? 

Answer : A

Read the passage given below and answer the following questions from 41 to 45. The table given below shows six organic compounds A, B, C, D, E and F having different molecular formula : 

Question. Identify the correct statements.
(a) A and F are saturated hydrocarbons while all others are unsaturated hydrocarbons.
(b) C and D belong to a homologous series having general formula CnH2n.
(c) B and E are alkynes.
(d) All the compounds have same physical and chemical properties. 

Answer : A

Question. Compound B is
(a) an alkane
(b) an alkene
(c) an alkyne
(d) none of these.

Answer : B

Question. Compound (F) has a general formula
(a) C_nH_{2n – 2}
(b) C_nH_2n
(c) C_nH_{2n + 4}
(d) C_nH_{2n + 2}

Answer : D

Question. Which of the following compounds belong to same homologous series?
(a) E and F
(b) B and C
(c) A and B
(d) C and D

Answer : D

Question. Which of the following is the member of the same homologous series as E?
(a) D
(b) A
(c) F
(d) B

Answer : D

Read the passage given below and answer the following questions . 

Question. Which of the following compounds is unsaturated hydrocarbon?
(a) S
(b) Q
(c) U
(d) R

Answer : C

Question. Which of the following compounds belongs to alkane series?
(a) P
(b) S
(c) T
(d) U

Answer : B

Question. Which of the following compounds belong to same homologous series?
(a) S and T
(b) T and U
(c) P and U
(d) P and T

Answer : D

Question. The functional group of compound (R) is
(a) alcohol
(b) aldehyde
(c) ketone
(d) carboxylic acid.

Answer : A

Question. Compound (T) belongs to homologous series of
(a) alkynes
(b) alkenes
(c) alkanes
(d) none of these.

Answer : A

Read the passage given below and answer the following questions from . An organic molecule has the following structure : 

Question. Which is the third member of this series?
(a) C₃H₇OH
(b) C₄H₉OH
(c) C₂H₅OH
(d) CH₃OH

Answer : A

Question. Which is the second member of this series?
(a) Ethanol
(b) Methanol
(c) Propanol
(d) Butanol

Answer : A

Question. To which homologous series does this molecule belong?
(a) Aldehydes
(b) Ketones
(c) Alcohols
(d) Alkanes

Answer : C

Question. What is the general formula of this homologous series?
(a) C_nH_{2n + 1}OH
(b) C_nH_{2n +} 2
(c) C_nH_2nO
(d) C_nH_{2n + 1}CHO

Answer : A

Question. Which is the next member of this series? 
(a) C₄H₉OH
(b) C₃H₇OH
(c) C₅H₁₁OH
(d) C₆H₁₃OH

Answer : C