CBSE Class 10 Chemistry Periodic Classification of Elements Worksheet Set E

Question. The early attempts to classify elements were based on -
(A) atomic number
(B) atomic mass
(C) electronic configuration
(D) None of these
Answer : B

Question. According to Newlands’ law of octaves 3rd element will resemble in its properties to -
(A) ninth element
(B) eighth element
(C) tenth element
(D) eleventh element
Answer : C

Question. The difference between ions and atoms is of -
(A) relative size
(B) electronic configuration
(C) presence of charge
(D) All of these
Answer : D

Question. Cl, Br, I, if this is a Dobereiner’s triad and the atomic masses of Cl and I are 35.5 and 127 respectively, then the atomic mass of Br is -
(A) 162.5
(B) 91.5
(C) 81.25
(D) 45.625
Answer : C

Question. Mendeleev classified elements in -
(A) increasing order of atomic number.
(B) increasing order of atomic masses.
(C) decreasing order of atomic masses.
(D) decreasing order of atomic number.
Answer : B

Question. All the members in a group of long form of periodic table have the same -
(A) valency
(B) number of valence electrons
(C) chemical properties
(D) All of these
Answer : D

Question. Which of the following elements has maximum metallic character ?
(A) Li
(B) N
(C) Na
(D) P
Answer : C

Question. Modern periodic law was proposed by-
(A) Mendeleev
(B) Henry Moseley
(C) Werner
(D) Bohr and Bury
Answer : B

Question. In the third period of the periodic table, the element having smallest size is -
(A) Na
(B) Ar
(C) Cl
(D) Si
Answer : C

Question. An element M has an atomic number 9 and atomic mass 19. Its ion will be represented by-
(A) M
(B) M+2
(C) M–
(D) M–2
Answer : C

Question. Newlands could classify elements correctly only upto -
(A) copper
(B) chlorine
(C) calcium
(D) chromium
Answer : C

Question. The long form of periodic table consists of -
(A) seven periods & eight groups.
(B) seven periods & eighteen groups.
(C) eight periods & eighteen groups.
(D) eighteen periods & eight groups.
Answer : B

Question. Which of the following pairs of elements belong to the same period of the periodic table ?
(A) C, Mg
(B) N, Ar
(C) Ca, Cl
(D) K, Cu
Answer : D

Question. The number of elements in the 4th period of periodic table are -
(A) 8
(B) 18
(C) 10
(D) 32
Answer : B

Question. Which of the following is the most reactive halogen ?
(A) F
(B) Cl
(D) Br
(D) I
Answer : A

Assertion and Reasoning Based Questions

Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : Periodicity in elements is the basis for the periodic table.
Reason : Henry Mosley gave the modern periodic law.
Answer : (b) 

Question. Assertion : Chlorine is less electronegative than fluorine.
Reason : It is because of its small size.
Answer : (b) 

Question. Assertion : Sodium is a metal whereas sulphur is a nonmetal.
Reason : From left to right metallic character decreases.
Answer : (a) 

Question. Assertion : Mendeleev’s periodic table was not widely accepted.
Reason : It is because hydrogen was not placed properly.
Answer : (b) 

Question. Assertion : Across a period atomic radius decreases.
Reason : It is because electron is added to the same shell.
Answer : (a) 

Creating Based Questions

Question. (a) The electronic configuration of an atom is 2, 8, 7.
Give its atomic number, nature of oxide.
(b) An element has an atomic number of 15 with which of the following elements will it show similar chemical properties :
(a) Be (4), (b) Ne (10), (c) N (7), (d) O (8).
(c) What will be the group number and period number respectively of an element X with atomic number 8 ?
Answer :
(a) Atomic number is 17. As it is a non-metal, it will form acidic oxide.
(b) The electronic configuration of element with atomic number 15 will be : 2, 8, 5 and from the given options, N (7) has the similar electronic configuration : 2, 5. So, N will show similar chemical properties.
(c) The electronic configuration of the element X would be 2, 6. Now, as there are 6 electrons in outer shell, it will be placed in 6th group and as there are only two shells filled with electrons, it will be placed in 2nd period.

Question. An element X forms a chloride with the formula XCl₂, which is a solid with a high melting point. Predict the most likely outer orbital electronic configuration of X and also name two more elements from same group of the Periodic Table to which elements X belongs.
Answer : The element X has 2 electrons in outer orbital as it forms a dichloride (XCl₂). So, this element belongs to group 2 of periodic table. Other elements of group 2 are magnesium (Mg) and beryllium (Be).

Question. Oxygen (atomic number 8) and sulphur (atomic number 16) belong to group 16 of the periodic table.Write the electronic configuration of the two elements.Which of them will be more electronegative ? Why ?
Answer :
Oxygen has atomic number 8, electronic configuration will be → 2, 6.
Sulphur has atomic number 16, electronic configuration will be → 2, 8, 6.
Oxygen with two shells will be more electronegative because it can easily gain electron due to its smaller size of atom, the nuclear charge attracts the electron easily to become negative ion.

Question. Write the contrasting points present in modern periodic table, against the following given points of Mendeleev’s table :
(a) Elements arranged according to atomic mass.
(b) It has 8 groups and 6 periods.
Answer :
The contrast points can be written as :
(a) In modern periodic table the elements are arranged according to atomic number.
(b) Modern periodic table has 18 groups and 7 periods.

Question. Write the atomic numbers and names of following elements :
(a) An element whose atom has 3 shells with 4 electrons in outermost shell.
(b) An element whose atom has twice as many electrons in its second shell as in its first shell ?
Answer :
(a) The electronic configuration can be written as 2, 8,4 here. So, the atomic number would be 14 and the element is silicon (Si).
(b) First shell has 2 electrons; hence second shell would have 4 electrons. So, the electronic configuration becomes 2, 4 and hence the atomic number is 6 and the element is carbon.

Case Study Based Questions

1. S.No. Atoms Mass number
1. Carbon 12
2. Helium 4
3. Oxygen 16
4. Neon 20
5. Sulphur 32

Question. What is the period and group of Sulphur ?
Answer : Period: 3
Group: 16

Question. What is the electronic configuration of neon ?
Answer : The electronic configuration is 2,8.

Question. Calculate the number of protons present in helium.
Answer : The atomic number of an atom is equal to its number of electrons and protons. Therefore, the number of protons present in helium is equal to its atomic number that is 2.

Question. What is the chemical formula formed by carbon and oxygen ?
Answer : The chemical formula is such that :
Carbon: 2,4
Oxygen: 2,6
Then, formula is: CO₂
 

2. Read the following and answer any four questions :

The term atomic size refers to the radius of an atom.The atomic size may be visualised as the distance between the centre of the nucleus and the outermost shell of an isolated atom. The atomic radius of hydrogen atom is 37 pm (picometre, 1 pm = 10^–12m).

Question. What is atomic radius?
(a) Distance between two adjacent electrons of an atom of an element.
(b) Shortest distance between the nucleus and the outermost shell of an atom.
(c) The circumference of the outermost shell of the atom.
(d) The circumference of the nucleus of the atom.
Answer : B

Question. If the atomic radius of Helium is 1.4 × 10^–10 m, then what is its atomic size?
(a) 1.4 pm
(b) 14 pm
(c) 140 pm
(d) 1400 pm
Answer : C

Question. Calcium has bigger atomic radius than Cobalt. Why?
(a) Being in the same period, both have same number of shells, but the cobalt has bigger atomic number which reduces its atomic radius.
(b) Being in the same group, both have same number of shells, but the cobalt has bigger atomic number which reduces its atomic radius.
(c) Being in the same group, both have same number of valence electrons
(d) Calcium has bigger atomic number than cobalt which increases its atomic radius.
Answer : A

Very Short Answers Type Questions

Question. Define electropositivity. 
Answer : Electropositivity is the measure of the ability of elements (mainly metals) to donate their valence electrons to form positive ions. The elements that can easily lose electrons to form positive ions are called electropositive elements. For example : Metals such as aluminium, sodium etc.

Question. The atomic radii of first group elements are given below :
Group-I element     Atomic Radii (pm)
  Na                                 86
  K                                   231
  Rb                                244
  Cs                                282
State the reason behind the observed trend in the above elements. 
Answer :
The above trend is observed because the atomic radii increases down the group, because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so that the atomic size increases in spite of the increase in nuclear charge.

Question. The electronic configuration of an element is 2, 8, 4.
State its :
(a) group and period in the Modern Periodic Table.
(b) name and write its one physical property.
Answer :
(a) Si = 2, 8, 4
(i) It means that it belongs to 3rd period and 14th group.
(ii) The name of element is Silicon.
(b) It is a metalloid. (i.e., element that has properties of botsh metals and non-metals).

Question. Give the number of a group in which metallic, metalloid and non-metallic, all three types of elements, are present.
Answer : Group 14.

Question. State Modern Periodic Law of classification of elements.
                              OR
How many vertical columns are there in the Modern
Periodic Table and what are they called ?
                              OR
State Modern Periodic Law. What is number of groups and periods in the Modern Periodic Table ?
Answer : “Properties of elements are a periodic function of their atomic number”. There are 18 groups and 7 periods are there in the Modern Periodic Table.

Question. The atomic number of an element is 17. To which group and period does this element belong ? Determine its valency. 
Answer : Element with atomic number 17 belongs to Group 17 and 3 period and its valency is 1.

Short Answers Type Questions

Question. (a) An element X has mass number 40 and contains 21 neutrons in its atom. To which group of the periodic table does it belong ?
(b) The element X forms a compound X2Y. Suggest an element that Y might be and give reasons for your choice.
Answer :
(a) Group 1 (2, 8, 8, 1).
(b) Oxygen (X is monovalent so Y has to be divalent to form the compound X2Y).

Question. Give reasons for the following :
(a) Noble gases do not react with other elements.
(b) Atom is electrically neutral but still it has a tendency to form an ion.
Answer :
(a) Elements react in order to complete its octet. Noble gases have complete octet. Therefore, they do not react with other elements.
(b) The elements have valence electrons. Metals have less valence electrons and give out the valence electrons to form cations to complete the outermost shell and attain nearest noble gas configuration. Likewise, non metals attain electrons to form anions to complete the outermost shell and attain nearest noble gas configuration.

Question. Write the electronic configurations of two elements P (atomic number 17) and Q (atomic number 19) and determine their group numbers and period numbers in the Modern Periodic Table. 
Answer :
Electronic configuration of ‘P’ : 2,8,7
Group number : 17
Period number : 3
Electronic configuration of Q : 2,8,8,1
Group number : 1
Period number : 4

Question. Consider the following elements (atomic numbers are given in parenthesis)
Ca(20) ; K(19) ; F(9) ; Be(4)
(a) Select :
(i) the element having one electron in the outermost shell
(ii) two elements of the same group. Write the number of this group.
(b) Write the formula of the compound formed by the union of Ca(20) and the element X(2, 8, 7).
Answer :
(a) (i) K
(ii) Be and Ca, Group-2
(b) CaX₂

Question. An element ‘M’ has atomic number 12.
(a) Write its electronic configuration and valency.
(b) Is ‘M’ a metal or a non-metal ? Give reason in support of your answer.
(c) Write the formula and nature (acidic / basic) of the oxide of M.
Answer :
(a) Electronic configuration of element ‘M’ is 2, 8, 2 and valency is 2.
(b) M is a metal because there are two electrons in its outermost shell and it easily loses the electron to form a positive ion.
(c) The formula of the oxide of M is MO and it is basic in nature.

Question. How does the atomic radius of the elements change on going
(a) from left to right in a period, and
(b) down a group in the Modern Periodic Table ?
Give reason in support of your answer.
Answer :
(a) Atomic radius decreases from left to right in a period because Nuclear charge increases which tends to pull the electrons closer to the nucleus.
(b) Atomic radius increases down a group because the number of shells increases on going down the group.

Question. The atomic number of an element M is 19.
(a) Write electronic configuration and valency of this element.
(b) Is ‘M’ a metal or a non-metal ? Give reason in support of your answer.
(c) Write the formula and nature (acidic/basic) of the oxide of M. 
Answer :
(a) Electronic configuration of element ‘M’ is 2, 8, 8, 1 and Valency is 1.
(b) M is a metal because it has 1 valence electron which it easily loses to form a positive ion.
(c) The formula of the oxide of M is M₂O, and it is basic in nature.

Question. Explain, giving reason, why carbon neither forms C⁴⁺ cations nor C^4– anions, but forms covalent compounds which are bad conductors of electricity and have low melting point and low boiling point. 
Answer : Carbon cannot lose 4 e^- to form C⁺⁴ cations, as very high energy is required to remove 4 e^– and also carbon cannot gain 4 e– to form C^–4 anions as nucleus with 6 protons cannot hold 10 electrons. Therefore, it can share 4e^– to form covalent compounds.
Carbon compounds do not conduct electricity being non polar and do not form ions or charged particles.
Due to weak intermolecular forces of attraction, carbon compounds have low melting points and boiling points.

Question. The atomic number of an element is 20.
(a) Write its electronic configuration and determine its valency.
(b) Is it a metal or a non-metal ?
(c) Write the formula of its chloride.
(d) Is it more reactive or less reactive than Mg (atomic number 12) ? Give reason for your answer.
Answer :
(a) Electonic configuration of X(20) is 2, 8, 8, 2
Valence electrons-2
Hence, valency is 2.
(b) It is a metal.
(c) XCl₂.
(d) It is more reactive than Mg as reactivity increases down the group since Mg is in III Period and X20
( Ca) is in IV period.

Question. The atomic number of an element is 19.
(a) Write the electronic configuration of this element and determine (i) the valency of this element and (ii) whether this element is a metal or a nonmetal.
(b) Write the formula of the oxide of this element.
(c) Is this element more reactive or less reactive than Na (atomic number 11) ? Justify your answer giving example. 
Answer :
(a) Electronic configuration of X(19) is 2, 8, 8, 1 and its.
(i) Valency is 1.
(ii) X is a metal.
(b) X₂O.
(c) X is more reactive than Na. X and Na belong to the same group. But Na is in the third period and X is in the fourth period. Since reactivity increases down the group X is more reactive than Na.

Question. The atomic number of an element is 12.
(a) Write its electronic configuration and determine its valency.
(b) Is it more reactive or less reactive than Ca (atomic number 20) ? Justify your answer giving reason.
(c) Is it a metal or a non-metal ?
(d) Write the formula of its oxide. 
Answer :
(a) Electronic configuration of X(12) is 2, 8, 2 and its valency is 2.
(b) Less reactive than Ca as reactivity increases down the group.
(c) It is a metal.
(d) Formula of its oxide is XO.

Question. State the main aim of classifying elements. Which is the more fundamental property of elements that is used in the development of Modern Periodic Table ? Name and state the law based on this fundamental property. On which side of the periodic table one can find metals, non-metals and metalloids ?
Answer : Main aim of classification of elements is the systematic study of the known elements. Atomic number is the more fundamental property of elements that is used in the development of the modern periodic table. ‘‘Properties of the elements are a periodic function of their atomic numbers.’’
Metal on the left, non-metal on the right and metalloids at the border of metals and beginning of non-metals.

Question. An element ‘X’ belongs to third period and second group of the Modern Periodic Table.
(a) Write its electronic configuration.
(b) Is it a metal or non-metal ? Why ?
(c) Write the formula of the compound formed when ‘X’ reacts with an element (i) Y of electronic configuration 2, 6 and (ii) Z with electronic configuration 2, 8, 7.
Answer :
(a) Electronic configuration of X is 2, 8, 2.
(b) X is metal, as it can easily loose electrons (from outer most orbit)
(c) (i) X Y    (ii) X Z
         2 2          2 1
Compound — XY Compound — XZ₂

Question. The atomic number of an element ‘X’ is 19.
(a) Write its electronic configuration.
(b) To which period of the Modern Periodic Table does it belong and what is its valency ?
(c) If ‘X’ burns in oxygen to form its oxide, what will be its nature – acidic, basic or neutral ?
(d) Write balanced chemical equation for the reaction when this oxide is dissolved in water.
Answer :
(a) Electronic Configuration of X (19) is 2,8,8,1.
(b) Fourth period, and its valency is 1.
(c) Basic oxide (X₂O) will be formed.
(d) X₂O + H₂O   →  2XOH

Question. How does the tendency of the elements to lose electrons change in the Modern Periodic Table in (a) a group, (b) a period and why ?
Answer :
(a) Increases down a group because at each succeeding element down a group the number of shells increases, so the distance of the valence shell from the nucleus increases, the effective nuclear force of attraction decreases on the last shell electrons decreases ,so it becomes easy for the atom to loose electrons.
(b) Decreases in a period left to right, because as the effective nuclear charge on the valence shell electron increases, the attraction between the valence electron and nucleus increases, so it becomes difficult to lose electrons.

Long Answers Type Questions

Question. (a) List any three observations which posed a challenge to Mendeleev’s Periodic law.
(b) How does the metallic character of elements vary on moving from
(i) left to right in a period,
(ii) from top to bottom in a group of the Modern Periodic Table ?
Give reason for your answer.
Answer :
(a) Three observations which posed a challenge to Mendeleev’s periodic law are :
(i) The position of isotopes could not be explained.
(ii) Wrong order of atomic masses of some elements could not be explained.
(iii) A correct position could not be assigned to hydrogen in the periodic table.

(b) (i) On moving from left to right in a period, the metallic character of elements decreases because electropositive character decreases due to increase in nuclear charge and decrease in atomic radius which causes nucleus to hold electrons more tightly.
(ii) On going down in a group of the periodic table, the metallic character of elements increases because electropositive character of elements increases with the increase in size of the atom.

Question. The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7, electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. Write the electronic configuration of the atoms of B and D, and the molecular formula of the compound formed when B and D combine.
Answer :
A — 1^st group.
B – 13^th group.
C – 15^th group.
D – 17^th group.
Electronic configuration
B → Atomic number = 13.
K L M
2 8 3
D → Atomic number = 17
K L M
2 8 7

Question. The electronic configuration of three elements A. B and C is given below :
A = 2. B = 2, 6 C = 2, 8, 2
(a) Which element belongs to the second period ?
(b) Which one of them is a noble gas ?
(c) What is the valency of B ?
(d) Name the element C.
(e) Which is a metal ?
Answer :
(a) B belongs to second period as its valency is two.
(b) A( 2= helium) is a noble gas.
(c) 2 (8-6).
(d) Magnesium (At. No. 12)
(e) C is a metal.

Question. (a) What was the basis of Mandelẽev’s classification of elements ?
(b) List two achievements of Mandelẽev’s periodic tables.
(c) List any two observations which posed a challenge to Mandelẽev’s periodic law.
Answer :
(a) Atomic mass was the basis of Mendeleev’s classification of elements.
(b) Achievements of Mendeleev’s periodic table are :
(i) He could classify all the 63 elements known at that time.
(ii) He left gaps for the yet to be discovered elements.
(iii) He predicted the properties of such elements.
(c) Observations which posed a challenge to Mendeleev’s periodic law are :
(i) Position of isotopes.
(ii) Irregular increase in the atomic masses in going from one element to the next, making the prediction of undiscovered elements difficult.
(iii) Position of hydrogen.

Question. Why is atomic number considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table ? How does the metallic character of elements vary as we move (a) from left to right in a period and (b) top to bottom in a group in the modern periodic table ? Give reasons to justify your answers.
Answer : Atomic number is more important parameter than atomic mass as atomic number determines the number of valence electrons which decide the chemical
properties of an atom of an element. This, it is considered more appropriate.
(a) Metallic character decreases from left to right in a period, because the tendency to lose electrons decreases due to increased attraction between nucleus and valence electrons.
(b) Metallic character increases down the group, as the tendency to lose electrons increases, due to decreased attraction between nucleus and valence electrons because outermost electrons are farther away.

PERIODIC CLASSIFICATION OF ELEMENTS

Multiple choice questions (1 Mark)

1. What is common for elements of same group?

(a) same number of shells (b) same physical properties

(c) same number of protons (d) same number of valence electrons

2. Which one of the following elements has the maximum number of valence electrons?

(a) Na      (b)Al      (c) Si      (d) P

3. The electronic configuration of an element is 2, 8, 8, 2. The position of the element is:

(a) 1st period , 2ndGroup                  (b) 2nd period , 1stGroup

(c) 4th period , 2nd Group                 (d) 4th period , 4thGroup

4. On moving across a period from left to right , the size of the atom

(a) increases                                     (b) does not change appreciably

(c) decreases                                    (d) first decreases and then increases

5. Which one of the following is the characteristic of isotopes of an element:

(a) same atomic mass number          (b) same atomic number

(c) same physical properties             (d) same chemical properties

Short answer questions (1 mark)

1. Out of Li , C and N , which forms the most basic oxide and which forms the most acidic oxide?

2. i) State modern periodic law of classification of elements.

ii) Give the name and electronic configuration of the second alkali metal belonging to the third period.

3. What is common in the elements belonging to the same period in the periodic table?

4. Arrange the following in decreasing atomic size:

(1) Na , Mg , K (2) N , F ,O (3) N , S , P.

5. What do you understand by the term periodicity ? Is the periodicity in properties a function of valence electrons?

2Marks Questions

1. How does metallic character of the elements vary

(a) down a group               (b) across a period?

2. Element X with atomic number 3 combines with an element Y having atomic number 17 .Write the

i) formula of the compound between X & Y.

ii) formula of the oxide of X

3. What was the anomaly in finding place for isotopes in the Mendeleev’s periodic table? How could the Modern periodic table remove the anomaly?

4. What would be the nature of the oxides formed by the elements on :

(a) the left hand side of the periodic table

(b) the right hand side of the periodic table?

5. Name

i) two elements that can form dipositive cations.

ii) two elements that have completely filled outermost shell.

3 Marks Questions

1. The atomic number of elements A ,B , C , D and E are given below;

 From the above table ,answer the following questions;

(a) Which two elements are chemically similar?

(b) Which is an inert gas?

(c) Which element belongs to third period of the periodic table?

(d) Which element among these is a non-metal?

2. Na , Mg and Al are the elements having 1,2,3 electrons respectively in the outer most shell. Which of the elements:

(a) has the largest atomic radius?

(b) least reactive?

Justify your answer.

3. What are the achievements of Mendeleev’s Periodic table? The atomic number of Cl is 17. On the basis of this information, answer the

questions that follow:

(a) Write the electronic configuration of Cl.

(b) Find its valency.

(c) To which group and period does it belong?

5 Marks Questions

1. The position of elements A, B, C, D, E, F and G in the Modern Periodic Table is given as under.

(a) In which group are inert elements placed?

(b) What type of ions would B, C, E and F form?

(c) How many shells would A have?

(d) What is the similarity between A and D?

(e) Identify the most abundant element in the earth’s crust.

2. Given below are some elements of the modern periodic table:

4Be,9F,14Si,19K,20Ca

(a) Select the element that has one electron in the outermost shell. Write its electronic configuration.

(b) Select two elements that belong to the same group. Give reason for your answer.

(c) Select two elements that belong to the same period. Which one of the two has bigger atomic size?

3. Compare and contrast the arrangement of elements in Mendeleev’s and the Modern periodic table.

Assertion-Reason Questions ( 1 mark )

1. The following questions consists of two statements-Assertion (A) and Reason (R).

Answer these questions selecting the appropriate option given below:

(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.

Assertion(A): Elements in the same vertical column have similar properties.

Reason (R):Elements have periodic dependence upon their atomic number.

2. The following questions consists of two statements-Assertion (A) and Reason (R).

Answer these questions selecting the appropriate option given below:

(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.

Assertion(A): Fluorine has greater atomic radius than nitrogen.

Reason (R): Atomic radius decreases along a period.

Fill in the blanks ( FIB ) type questions ( 1mark )

Fill in the blanks with suitable words:

(a)The basis for modern periodic table is ---------

(b)The horizontal rows in a periodic table are called --------

(c)Group 17 elements are known as ---------

(d)The size of elements ----- in a group from top to bottom.

(e)According to Newlands’ classification of elements , the properties of sulphur are similar to those of oxygen because sulphur is the ----- element starting from oxygen.

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