CBSE Class 10 Science Periodic Table VBQs

VALUE BASED QUESTIONS

Unit - Periodic Classification of Elements

Std – X

Question. Aashish is a student of Class V. His class teacher gave him an assignment to write a review of any of the books written by Enid Blyton. He goes to the library but he was unable to locate anyone. He approaches the librarian for help. The librarian took him to one of the sections of the library and showed him many books of Enid Blyton.

CONTEXTUAL QUESTION : 

   (i) What helped the librarian to locate the book easily ?

VALUE BASED QUESTION :

   (ii) Mention any two values that Aashish learnt 

(i) Value Points

     1. awareness about classification

     2. Application of knowledge.

     3. orderliness

Question. Tanvi was reading the morning newspaper. She came across a new word. She wanted to know its meaning and the way it is pronounced. She refers the dictionary and was thrilled when her attempt was successful.

CONTEXTUAL QUESTION :

Which property of the dictionary helped her in locating the word easily? 

VALUE BASED QUESTION :

     (i) What values do you think that Tanvi has? 

Value Points

     1. Awareness about classification

     2. Application of knowledge.

Question. A particular school has house matches after the assembly on every Wednesday . There would be utter chaos before the matches since each class is divided into different houses. The P.T.Master approached the Principal and got permission to allow the students to assemble housewise on Wednesdays.

CONTEXTUAL QUESTION :

What is the reason for chaos before the matches? Relate this to any one method of periodic classification of elements. 

VALUE BASED QUESTION:

What values can be imbibed from the P.T.Master’s  suggestion ? 

Value Points (any two)

    1. Need for change with time

    2. Capability to find alternative solution.

    3. Simplifying work

Question. Mendeleev left some gaps in his periodic table and predicted the discovery of new elements. Even though it was a drawback he boldly presented his table.

CONTEXTUAL QUESTION :

What is your view about Mendleev’s decision? 

VALUE BASED QUESTION :

List any any two values learnt from Mendleev ‘s decision 

Value Points

1. Self - confidence

2. Courage to face situations.

Question. The teacher was explaining the properties of elements, the types of bonding in the class. After that she asked the children the position they preferred in the periodic table if the choice is given as 14 th group or 18th group. Some chose14th and some18th.

CONTEXTUAL QUESTION :

       (i) Compare the properties of group 14 and group 18 elements.

VALUE BASED QUESTION :

      (ii) Mention the value points for those who chose group 14 and group 18. 

Value Points

Group 14 – sharing and caring, friendliness 

Group 18 - independent, staying calm and composed in all situations.

Question. 14 elements after actinium is called
(a) Lanthanides
(b) Actinides
(c) d-block elements
(d) p-block elements
Answer : B

Question. An element belongs to period 2 and group 2 the number of valence electrons in the atoms of this element is
(a) 2
(b) 4
(c) 3
(d) 1
Answer : A

Question. Which of the given elements A, B, C, D, and E with atomic number 3, 11, 15, 18, 19 respectively belong to the same group
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) A, B, E
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 : B

Question. Element belonging to which of the following atomic numbers 11, 19, 14, 18, 23 belong to the same period?
(a) 11, 14, 23
(b) 11, 18, 20
(c) 11, 14, 18
(d) 14, 19, 23
Answer : C

Question. Electronic configuration of Al+3 is
(a) 2, 8, 3
(b) 2, 8, 8
(c) 2, 8
(d) 2, 8, 8, 3
Answer : C

Question. Which of the following sets does not belong to a group?
(a) Li, Na, K
(b) B, C, N
(c) B, Al, Ga
(d) O, S, Se
Answer : B

Question. Mendeleev predicted the existence of two elements and named them as eka-silicon and eka-aluminium. Identify the elements which took their position at later stage
(a) Si and Ge
(b) Si and Ga
(c) Ge and Ga
(d) Si and Al
Answer : C

Question. An element with atomic number will form a basic oxide _________.
(a) 7
(b) 17
(c) 14
(d) 11
Answer : D

Question. 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)
Answer : C

Question. The correct order of the increasing radii of the elements Na, Si, Al and P is
(a) Si, Al, P, Na
(b) P, Si, Al, Na
(c) Al, Si, P, Na
(d) Al, P, Si, Na
Answer : B

Question. Two elements X and Y have —
(i) X has 17 protons 18 neutrons
(ii) Y has 17 protons and 20 neutrons Both X and Y are—
(a) Isobars
(b) Isotopes
(c) Isotones
(d) None of the above
Answer : B

Question. Identify the group which is not a Döbereiner triad
(a) Li, Na, K
(b) Be, Mg, Cr
(c) Ca, Sr, Ba
(d) Cl, Br, I
Answer : B

Question. The group number and period number respectively of an element with atomic number 8 is
(a) 6, 2
(b) 16, 2
(c) 6, 8
(d) 16, 4
Answer : A

Question. The increasing order of the atomic radii of elements Na, Rb, K, Mg is
(a) Na < K < Mg < Rb
(b) K < Na < Mg < Rb
(c) Na < Mg < K < Rb
(d) Mg < Na < K < Rb
Answer : C

Case Study Questions Periodic Classification of Elements Class 10 Science

Read the passage given below and answer the following questions from Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the modern periodic table :  

Question. Element E forms a chloride with formula  
(a) E Cl₂
(b) E Cl₃ 
(c) E Cl₄
(d) ECl

Answer : C

Question. Which of the following elements is a metalloid?  
(a) A
(b) B
(c) C
(d) E

Answer : D

Question. Which element in the given table has same number of electrons as in K+ and Cl–?  
(a) C
(b) F
(c) E
(d) D

Answer : B

Question. The formula of the oxide of element D will be  
(a) DO
(b) D₂O
(c) D₂O₃
(d) D₂O₅

Answer : C

Question. Which of the following elements has most metallic character?  
(a) F
(b) D
(c) E
(d) B

Answer : B

Read the passage given below and answer the following questions from In 1913, Henry Moseley showed that the atomic number of an element is the more fundamental property than its atomic mass. Accordingly, Mendeleev’s periodic law was modified and atomic number was adopted as the basis of modern periodic table. In this periodic table, the elements are arranged in increasing order of their atomic numbers. There are 18 vertical columns in the periodic table which constitute 18 groups or families. The groups are numbered as 1, 2, 3, ... upto 18. All the members of a particular group have similar outer shell electronic configuration. There are seven horizontal rows of the periodic table which are known as periods.

Question. In the periodic table, the element with atomic number 16 will be placed in the group  
(a) fourteen
(b) sixteen
(c) thirteen
(d) fifteen.

Answer : B

Question. All the elements in a period in the periodic table have the same 
(a) atomic number
(b) electronic configuration
(c) atomic weight
(d) valence shell.

Answer : D

Question. Which of the following combinations of elements belong to the same group?   
(a) N, P, S
(b) Li, Na, K
(c) Na, Mg, Al
(d) O, S, Cl

Answer : B

Question. The atoms of elements belonging to the same group of periodic table have same number of  
(a) protons
(b) electrons
(c) neutrons
(d) electrons in outermost shell.

Answer : D

Read the passage given below and answer the following questions from Maximum number of electrons that can be accommodated in a shell is given by the formula : 2n2, where n is the number of the outermost from the nucleus. For example, K shell – 2 × (1)2 ⇒ 2, hence, K-shell can accommodate maximum 2 electrons. L shell – 2 × (2)2 ⇒ 8, hence, L-shell can accommodate maximum 8 electrons. In the modern periodic table, elements are placed according to their electronic configuration. The elements present in any group have the same number of valence electrons. The elements present in any period contain the same number of shells. The first period of the modern periodic table corresponds to the filling of electrons in the first energy shell, i.e., K-shell, first period has two elements. The second period of the periodic table corresponds to the filling of electrons in the second energy shell, i.e., L-shell, second period contains eight elements. The third, fourth, fifth, sixth and seventh periods have 8, 18, 18, 32 and 32 elements respectively.

Question. The elements A, B, C and D have atomic numbers 4, 12, 17 and 19 respectively. Which pair of elements belong to the same period?  
(a) B and C
(b) A and B
(c) A and D
(d) C and D

Answer : A

Question. Which of the following have the same number of electrons in outermost shell?  
(a) Elements with atomic numbers 3, 11, 19
(b) Elements with atomic numbers 14, 15, 16
(c) Elements with atomic numbers 12, 20, 28
(d) Elements with atomic numbers 10, 18, 26

Answer : A

Question. Electronic configuration of an element ‘X ’ is 2, 1. The number of elements present in the period to which ‘X ’ belongs is  
(a) 8
(b) 32
(c) 18
(d) 2

Answer : A

Question. Among the given elements A, B, C, D and E with atomic numbers 2, 3, 7, 10 and 30 respectively, which of these belong to the same period?  
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E

Answer : B

Question. Which of the following elements has two shells and both are completely filled?  
(a) Helium
(b) Neon
(c) Calcium
(d) Fluorine

Answer : B

Read the passage given below and answer the following questions from Mendeleev arranged the 63 elements known at that time in order of their ascending atomic masses and prepared a periodic table. Mendeleev’s periodic table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’. Elements with similar properties were placed in same groups. The basis of Mendeleev’s classification is his periodic law which states that :
(I) Atomic mass is the fundamental property of elements.
(II) The physical and chemical properties of elements are periodic function of their atomic masses.

Question. The properties of eka-aluminium predicted by Mendeleev were the same as properties of which element that was discovered later?  
(a) Scandium
(b) Germanium
(c) Gallium
(d) Aluminium

Answer : C

Question. Which of the following statements is not correct about Mendeleev’s periodic table?  
(a) In the Mendeleev’s periodic table, some places were left vacant for new elements which were not discovered at that time.
(b) Group VIII like groups I-VII has been divided into two sub-groups A and B.
(c) The group of an element in the periodic table represents its valency.
(d) Li and C belong to same period in Mendeleev’s periodic table.

Answer : B

Question. Which of the following metals is not placed in eighth group of Mendeleev’s periodic table?  
(a) Fe
(b) Na
(c) Co
(d) Ni

Answer : B

Question. In Mendeleev’s periodic table, silver belongs to IB group. The group to which silver belongs in the modern periodic table is  
(a) first
(b) eleventh
(c) tenth
(d) sixteenth.

Answer : B

Question. In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later?  
(a) Chlorine
(b) Silicon
(c) Oxygen
(d) Germanium

Answer : D

Read the passage given below and answer the following questions from The distance between the centre of the nucleus and the outermost shell of electrons is known as atomic radius. On moving from left to right along a period, atomic radii decrease because effective nuclear charge increases. For example, the atomic size decreases regularly from Li to F in the second period and from Na to Cl in the third period. It may, however, be noted that in any period, the noble gas has the largest size. On moving down in a group, atomic radii increase. 

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. Among O, C, F, Cl, Br, the correct order of increasing atomic radii is   
(a) F, O, C, Cl, Br
(b) F, C, O, Cl, Br
(c) F, Cl, Br, O, C
(d) C, O, F, Cl, Br

Answer : A

Question. Which of the following has the maximum atomic radius?  
(a) Al
(b) Si
(c) P
(d) Mg

Answer : D

Question. The element with the smallest size in group 13 is  
(a) gallium
(b) thallium
(c) aluminium
(d) boron.

Answer : D

Question. The atomic radius decreases as we move across a period because  
(a) atomic mass increases
(b) atomic number decreases
(c) effective nuclear charge increases
(d) electrons are removed.

Answer : C

Very Short Answer Type Questions

Question. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table? (any two)
Answer: Germanium, Scandium.

Question. Write any one difference in the electronic configurations of group 1 and group 2 elements.
Answer: Group 1 elements have one electron in their outermost shell while group 2 elements have two electrons in their outermost shell.

Question. N, O, F cannot be classified as Döbereiner’s triad. Why?
Answer: Although the atomic mass of O (16 u) is approximately an average (16.5 u) of the atomic masses of N (14 u) and F (19 u), i.e., (14 + 19)/2 = 16.5 but they cannot be regarded as a Döbereiner’s triad because their properties are altogether different.

Question. Why does atomic size decrease as we move from left to right along a period in the periodic table?
Answer: Effective nuclear charge increases as we move from left to right in the periodic table so atomic size decreases.

Question. Write the atomic numbers of two elements ‘X’ and ‘Y’ having electronic configurations 2, 8, 2 and 2, 8, 6 respectively.
Answer: Electronic configuration of X = 2, 8, 2
∴ Atomic number is 2 + 8 + 2 = 12
Similarly,
Electronic configuration of Y = 2, 8, 6
∴ Atomic number is 2 + 8 + 6 = 16

Question. Out of Li and K which will have stronger metallic character and why?
Answer: Potassium (K) will have stronger metallic character than lithium (Li) because as we move from top to bottom in a group, the size increases which increases the ease of liberation of electrons.

Question. Name two elements which show same kind of chemical reactivity as sodium.
Answer: Lithium (Li) and potassium (K) both belong to the same group as sodium (Na), So, they will show the same chemical properties as sodium.

Question. What is the valency of silicon with atomic number 14?
Answer: Atomic number of silicon = 14
Electronic configuration = 2, 8, 4
As silicon (Si) contains four electrons in its outermost shell, its valency will be four.

Question. Write the number of horizontal rows in the Modern Periodic Table. What are these rows called?
Answer: There are seven horizontal rows of elements in the Modern periodic table which are known as periods.

Question. State the Modern periodic law of classification of elements.
Answer: Modern periodic law states that the physical and chemical properties of elements are the periodic function of their atomic numbers.

Short Answer Type Questions :

Question. An element X has a total of 31 nucleons, out of which 16 are neutrons.
(a) Write the electronic configuration of an atom of element X.
(b) Determine the group and period number of element X.
(c) Give the formula of the ion formed by element X.
Answer: (a) Number of protons = 31 – 16 = 15
Number of electrons = 15
Electronic configuration = 2,8,5
(b) Element X has five valence electrons.
Hence, element X is from Group V.
Element X has three occupied shells.
Hence, element X is in Period 3.
(c) Formula of the ion formed by X = X 3–

Question. Give reason – While going down in group 1 lithium is least electropositive while caesium is most electropositive.
Answer: As we move down in a group, an electron shell is added after every change of period. For example, lithium has only two electron shells around the nucleus, but caesium has six electron shells around the nucleus. Thus, the positive charge within the nucleus holds the valence electrons of lithium more strongly than caesium. In other words, the valence electrons are held very loosely in case of caesium than lithium. Thus, caesium can lose its valence electrons more easily and hence, is more electropositive as compared to lithium, which is less electropositive. In other words, caesium is more metallic in character than lithium.

Question. In the Modern Periodic Table, the element calcium (atomic number = 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these elements have physical and chemical properties resembling those of calcium and why?
Answer: From the given data, the electronic configuration of different elements can be written as :
Calcium (20) = 2, 8, 8, 2
Element with atomic number 12 = 2, 8, 2
Element with atomic number 19 = 2, 8, 8, 1
Element with atomic number 21 = 2, 8, 8, 3
Element with atomic number 38 = 2, 8, 18, 8, 2
It can be easily seen that elements with atomic numbers 12 and 38 have two electrons in their outermost shell thus, they belong to same group as that of calcium. So, they will
show the physical and chemical properties resembling those of calcium.

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) The element belongs to group 14 and 3rd period of the Modern Periodic Table.
(b) The element is silicon. It is non-lustrous.

Question. Choose from the following :
₄Be, ₉F, ₁₉K, ₂₀Ca
(i) The element having one electron in the outermost shell.
(ii) Two elements of the same group.
Answer: The electronic configurations of the given elements are :
₄Be = 2, 2
₉F = 2, 7
₁₉K = 2, 8, 8, 1
₂₀Ca = 2, 8, 8, 2
(i) Potassium (K) has one electron in its outermost shell.
(ii) Be and Ca have two electrons in their outermost shells hence, they belong to same group.

Question. Three elements ‘X’, ‘Y’ and ‘Z’ having atomic numbers 11, 7 and 6 respectively react with oxygen to form their oxides.
(a) Arrange these oxides in increasing order of their basic nature.
(b) Give reason for your answer.
Answer: 11X = 2, 8, 1
7Y = 2, 5
6Z = 2, 4
(a) Y < Z < X
(b) X is metallic in nature hence, its oxide is basic in nature.
While Y and Z are non-metals and their oxides are acidic in nature.

Question. Potassium, bromine and krypton are elements in period 4 of the Periodic Table.
(a) In which group of the periodic table can these elements be found?
(i) Potassium (ii) Bromine (iii) Krypton
(b) Bromine exists as a molecule. Draw a ‘dotand- cross’ diagram to show the bonding in a molecule of bromine.
(c) Krypton does not react with either potassium or bromine. Explain the unreactive nature of krypton.
Answer: (a) (i) Group I (ii) Group 17 (iii) Group 18

(c) Krypton has a stable electronic configuration, with 8 electrons in its valence shell. Hence, it does not lose, gain or share electron(s) with another atom. 

Question. Elements magnesium and oxygen respectively belong to group 2 and group 16 of the Modern Periodic Table. If the atomic numbers of magnesium and oxygen are 12 and 8 respectively, draw their electronic configuration and show the process of formation of their compound by transfer of electrons.
Answer: Atomic number of magnesium = 12
∴ Electronic configuration = 2, 8, 2
Valency of magnesium (Mg) = 2
Similarly, for oxygen (O) atomic number = 8
Electronic configuration = 2, 6
Valency of oxygen = 8 – 6 = 2
Formation of their compound will be as follows : 

Question. Calcium is an element with atomic number 20. Stating reason answer each of the following questions :
(i) Is calcium a metal or non-metal?
(ii) Will its atomic radius be larger or smaller than that of potassium with atomic number 19?
(iii) Write the formula of its oxide.
Answer: Given that, atomic number of calcium is 20.
So, its electronic configuration = 2, 8, 8, 2
(i) As, it has 2 valence electrons in the outermost shell which can be easily lost, so it is a metal.
(ii) Atomic number of K (potassium) is 19 so, it is placed before Ca(20) in the same period.
On moving from left to right in a period, the atomic radius decreases.
Hence, atomic radius of Ca(20) will be smaller than that of K(19).
(iii) The valency of calcium as well as oxygen is 2 thus, the formula of the oxide will be CaO.

Question. What is meant by periodicity of properties of elements? Why are the properties of elements placed in the same group of the periodic table similar?
Answer: When elements are arranged in increasing order of their atomic numbers, elements with similar chemical properties are repeated at definite intervals. This is known as periodicity of properties of elements.
Elements placed in the same group of the periodic table have similar properties because they have same number of outermost electrons and hence, show same valency. Thus, they all will form similar type of compounds.

Long Answer Type Questions :

Question. (a) Consider three elements Na, Cl, Ar and answer the following.
(i) Discuss their metallic and non-metallic character.
(ii) Discuss the acid-base character of their oxides.
(b) The element with atomic number 14 is hard and forms acidic oxide and a covalent halide.
To which of the categories does the element belong?
Answer: (a) The electronic configurations of these elements are Na : 2, 8, 1 ; Cl : 2, 8, 7 and Ar : 2, 8, 8
(i) Sodium has only 1 electron in its valence shell which it can lose easily. Therefore it is a typical metal, chlorine has even electrons in its outermost shell, it can easily accept one
electron to get noble gas configuration, hence it is a typical non-metal. Ar is a noble gas.
(ii) The oxide of Na i.e. Na₂O dissolves in water to form NaOH which is a strong base. The oxide of chlorine i.e. Cl₂O7 dissolves in water to give HClO₄ which is a strong acid.
Ar does not form any oxides.
Na₂O + H₂O → 2NaOH
Cl₂O7 + H₂O → 2HClO₄
Hence, both metallic character of the elements and basic character of oxides decreases from left to right across a period.
(b) Non-metal, because it forms acidic oxide and covalent halide which are characteristics of non-metals.

Question. In the table given below, some of the elements of the periodic table with atomic numbers from 3 to 18 are given. These are represented by letters, which are not the usual symbols of the elements. 38
(a) Which of these
(i) is an alkaline earth metal?
(ii) are alkali metals?
(iii) is an element with valency 4?
(b) If A combines with F, what would be the formula of the resulting compound?
(c) What is the electronic arrangement of G?
Answer: (a) (i) C is an alkaline earth metal.
(ii) A and B are alkali metals.
(iii) D is an element with valency 4.
(b) If A combines with F, the formula of the resulting compound will be A+F –., i.e., AF.
(c) The electronic arrangement of G is 2, 8.

Question. (a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newlands and Mendeleev. List one advantage and one limitation of all the three attempts.
(b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.
(c) State Modern periodic law.
Answer: (a) Advantage of Dobereiner’s triads : It recognised a relationship between properties of elements and their atomic weights.
Limitation of Dobereiner’s triads : Dobereiner could identify only three triads. He was not able to prepare triads of all the known elements.
Advantages of Newland’s law of octaves : This law provided a basis for the classification of elements into groups of elements having similar properties.
Limitation of Newlands’ law of octaves : This law worked only for the lighter elements. All the element discovered at that time could not be classified into octaves.
Advantages of Mendeleev’s periodic table : He classified all the 63 elements discovered at that time on the basis of similarities in their properties.
Limitation of Mendeleev’s periodic table : Increasing order of atomic masses could not be maintained in all cases e.g., cobalt with higher atomic mass was placed before nickel.
(b) Henry Moseley, an English physicist, showed that atomic number of an element is a more fundamental property than its atomic mass.
(c) Modern periodic law states that the physical and chemical properties of elements are the periodic function of their atomic numbers.

Question. The table below shows the electronic configuration of six elements. 39
(a) Give the letter (s) of (i) two elements that are in the same period of the periodic table.
(ii) two elements that are in the same group of the periodic table.
(iii) a noble gas.
(iv) group VII non-metals.
(v) element which forms positive ion.
(b) (i) Give the formula of the compound formed between elements P and S.
(ii) What type of bonding would you expect in the compound formed?
Answer: (a) (i) P, Q and R (two electron shells) or S and T (three electron shells).
(ii) P and U (one valence electron) or R and S (seven valence electrons).
(iii) T (completely filled valence shell).
(iv) R or S (seven valence electrons).
(v) P or U (one valence electron).
(b) (i) PS
(ii) ionic bonding.

Question. (a) How does metallic character of elements in Modern Periodic Table vary on moving from
(i) left to right in a period
(ii) top to bottom in a group?
Explain with the help of an example in each case.
(b) If an element X is placed in group-14, what will be the nature of bond in its chloride?
Write the chemical formula of the compound formed.
(c) An element X has mass number = 35 and number of neutrons = 18. What is the atomic number of X? Write electronic configuration of X and determine its valency.
Answer: (a) In the Modern periodic table, there are 18 vertical columns called groups and 7 horizontal rows called periods.
Trend of metallic character :
(i) Along the period from left to right : Metallic character of elements decreases as we move from left to right in a period.
Metallic character depends on the electropositive character (tendency to lose electrons) of the elements. As we go across the period from left to right, one electron is added to same
shell at every stage which increases the effective nuclear charge and hence, valence electrons becomes more and more closer to the nucleus. Due to this, the tendency of atoms
to lose valence electrons and form positive ions decreases.
Hence, electropositive character decreases resulting in decrease of metallic character.
Example :
Variation of metallic character across the period : 

(ii) Down the group : Metallic character of elements increases on moving down the group as the electropositive character increases down the group.
Example :
Variation of metallic character down the group :
(b) Since element ‘X’ is placed in group 14, therefore, its valency is 14 – 10 = 4. Further, since it is difficult to either lose all the four valence electrons or gain four more electrons,
therefore, it prefers to share these four electrons to acquire the stable electronic configuration of the nearest inert gas.
Thus, the nature of the bond of chloride of element ‘X’ is covalent and the chemical formula is XCl4.
(c) Mass number of X = 35
Number of neutrons = 18
∴ Number of electrons = Number of protons
= (Mass number – Number of neutrons)
= 35 – 18 = 17
Number of electrons of X = Atomic number of X = 17
Thus, electronic configuration of X = 2, 8, 7
As it has 7 electrons in the outermost shell, so it belongs to 17th group. Moreover the electrons are present in three shells, so it belongs to 3rd period.
Valency of X = 8 – 7 = 1

Please refer to the link below for CBSE Class 10 Science VBQs - Periodic Table