Chapter 5. Periodic Classification of Elements Class 10 NCERT Exemplar Solutions (CBSE 2026 Guide)
Class 10 Science Chapter 5: Periodic Classification of Elements : NCERT Exemplar Solutions with Detailed Explanation
Chapter 5: Periodic Classification of Elements
Multiple Choice Questions
1. Upto which element, the Law of Octaves was found to be applicable
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium
Answer : (b) Calcium
[ The Law of Octaves was a periodic law formulated by John Newlands in the 19th century, which attempted to organize the known chemical elements at the time. According to this law, every eighth element displayed similar properties. The law was found to be applicable up to calcium. Therefore, the correct answer to your question is: (b) Calcium . ]
2. According to Mendeleev's′ Periodic Law, the elements were arranged in the periodic table in the order of
(a) increasing atomic number
(b) decreasing atomic number
(c) increasing atomic masses
(d) decreasing atomic masses
Answer : (c) increasing atomic masses .
[ According to Mendeleev's Periodic Law, the elements were arranged in the periodic table in the order of (c) increasing atomic masses. Mendeleev's periodic table was based on the increasing atomic masses of elements, and he organized the elements in rows and columns based on their chemical and physical properties.]
3. 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 perioidc table later
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon
Answer : (a) Germanium
[ The element that found a place in Mendeleev's Periodic Table later is: (a) Germanium ]
4. Which of the following statement (s) about the Modern Periodic
Table are incorrect
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses
(iii) Isotopes are placed in adjoining group (s) in the Periodic Table
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number
(a) (i) only (b) (i), (ii) and (iii)
(c) (i), (ii) and (iv) (d) (iv) only
Answer : (b) (i), (ii) and (iii)
[ The correct statement about the Modern Periodic Table is:
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.
Therefore, the incorrect statements are: (i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number. (ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses. (iii) Isotopes are placed in adjoining group (s) in the Periodic Table.
So, the correct answer is: (b) (i), (ii), and (iii) ]
5. Which of the following statements about the Modern Periodic Table is correct:
(a) It has 18 horizontal rows known as Periods
(b) It has 7 vertical columns known as Periods
(c) It has 18 vertical columns known as Groups
(d) It has 7 horizontal rows known as Groups
Answer : (c) It has 18 vertical columns known as Groups
[ The correct statement about the Modern Periodic Table is: (c) It has 18 vertical columns known as Groups. So, the correct answer is (c). ]
6. Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
Answer : (b) B, C, D
[ The elements with atomic numbers 2, 3, 7, 10, and 30 are Helium (He), Lithium (Li), Nitrogen (N), Neon (Ne), and Zinc (Zn) respectively. These elements actually belong to the same period (period 2) in the periodic table. Therefore, the correct answer is: (b) B, C, D ]
7. The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Answer : (c) A and C
[ The elements in the same group have similar chemical properties, and elements in the same group have the same number of valence electrons.
In this case, elements A and C have atomic numbers 9 and 17, respectively. Both of these elements belong to Group 17 (also known as Group VIIA or the halogens) because they have the same number of valence electrons.
Therefore, the correct pair of elements belonging to the same group is: (c) A and C ]
8. Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table?
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
Answer : (c) Group 18
[ The electronic configuration 2,8 corresponds to the configuration of a noble gas. In this case, it is the electronic configuration of neon (Ne).
In the Modern Periodic Table, noble gases are found in Group 18. Therefore, the correct answer is: (c) Group 18 ]
9. An element which is an essential constituent of all organic compounds belongs to
(a) group 1
(b) group 14
(c) group 15
(d) group 16
Answer : (b) group 14
[ An element which is an essential constituent of all organic compounds is carbon. Carbon belongs to Group 14 in the Modern Periodic Table. Therefore, the correct answer is: (b) Group 14 ]
10. Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
Answer : (b) L shell .
[In the Modern Periodic Table, elements of period 2 have electrons filling the first and second shells. The outermost shell for elements of period 2 is the second shell. The second shell is denoted by the letter (b) L shell.
Therefore, the correct answer is: (b) L shell .]
11. Which one of the following elements exhibit maximum number of valence electrons?
(a) Na
(b) Al
(c) Si
(d) P
Answer : (d) P
[ Valence electrons are the electrons in the outermost shell of an atom. The number of valence electrons increases as you move from left to right across a period in the periodic table.
Among the given elements:
Sodium (Na) is in Group 1 and has 1 valence electron.
Aluminum (Al) is in Group 13 and has 3 valence electrons.
Silicon (Si) is in Group 14 and has 4 valence electrons.
Phosphorus (P) is in Group 15 and has 5 valence electrons.
Therefore, the element that exhibits the maximum number of valence electrons among the options is: (d) P (Phosphorus) with 5 valence electrons. ]
12. Which of the following gives the correct increasing order of the atomic radii of O, F and N ?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N
Answer : (d) F, O, N
[ The atomic radii generally decrease across a period from left to right on the periodic table. Among the given elements (Oxygen, Fluorine, and Nitrogen), they are in the same period (Period 2).So, the correct increasing order of atomic radii is from right to left: (d) F, O, N ]
13. Which among the following elements has the largest atomic radii?
(a) Na
(b) Mg
(c) K
(d) Ca
Answer : (c) K
[ Atomic radius generally increases down a group in the periodic table. The elements provided (Na, Mg, K, Ca) are all in the same group (Group 2).
Among these, the element with the largest atomic radius is at the bottom of the group. Therefore, the element with the largest atomic radius is: (c) K (Potassium) ]
14. Which of the following elements would lose an electron easily?
(a) Mg
(b) Na
(c) K
(d) Ca
Answer : (c) K
[ Yes, your observation is correct. Among the given options, potassium (K) in option (c) would lose an electron easily. Elements in Group 1 (alkali metals), such as potassium, have one electron in their outermost shell, making it easier for them to lose that electron and achieve a stable electron configuration. Therefore, the correct answer is: (c) K (Potassium) ]
15. Which of the following elements does not lose an electron easily?
(a) Na
(b) F
(c) Mg
(d) Al
Answer : (b) F
[ Among the given options, fluorine (F) in option (b) does not lose an electron easily. Fluorine belongs to Group 17 (halogens), and it has a tendency to gain electrons rather than lose them. Elements in this group typically have high electronegativity and are more likely to accept electrons to achieve a stable electron configuration. Therefore, the correct answer is: (b) F (Fluorine) ]
16. Which of the following are the characteristics of isotopes of an element?
(i) Isotopes of an element have same atomic masses
(ii) Isotopes of an element have same atomic number
(iii) Isotopes of an element show same physical properties
(iv) Isotopes of an element show same chemical properties
(a) (i), (iii) and (iv) (b) (ii), (iii) and (iv)
(c) (ii) and (iii) (d) (ii) and (iv)
Answer : (d) (ii) and (iv)
[ The characteristics of isotopes of an element are: (i) Isotopes of an element have the same atomic number. (ii) Isotopes of an element have different atomic masses. (iii) Isotopes of an element show the same chemical properties. (iv) Isotopes of an element may have slightly different physical properties. So, the correct option is: (d) (ii) and (iv) ]
17. Arrange the following elements in the order of their decreasing metallic character: Na, Si, Cl, Mg, Al
(a) Cl > Si >Al > Mg >Na
(b) Na >Mg >Al >Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na> Si > Ca> Mg
Answer : (b) Na >Mg >Al >Si > Cl
The correct order of decreasing metallic character among the given elements is: (b) Na > Mg > Al > Si > Cl ]
18. Arrange the following elements in the order of their increasing non-metallic character
Li, O, C, Be, F
(a) F < O < C < Be < Li
(b) Li < Be < C < O< F
(c) F < O < C < Be < Li
(d) F < O < Be < C < Li
Answer : (d) F < O < Be < C < Li
[ The correct order of increasing non-metallic character among the given elements is: (d) F < O < Be < C < Li ]
19. What type of oxide would Eka– aluminium form?
(a) 
(b) 
(c) 
(d) EO
Answer : (c)
[ Eka-aluminium refers to the element gallium (Ga). Gallium is located below aluminium (Al) in the periodic table. The general formula for the oxide of gallium is 
. Therefore, the correct option is: (c) ]
20. Three elements B, Si and Ge are
(a) metals
(b) non-metals
(c) metalloids
(d) metal, non-metal and metalloid respectively
Answer : (c) metalloids
[ The elements Boron (B), Silicon (Si), and Germanium (Ge) are metalloids. Metalloids have properties intermediate between metals and non-metals. Therefore, the correct option is: (c) metalloids. ]
21. Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19
Answer : (a) An element with atomic number 7
[ An acidic oxide is formed by a non-metallic element. Non-metals generally form acidic oxides.
Among the options given: (a) An element with atomic number 7 is nitrogen (N), which can form acidic oxides. (b) An element with atomic number 3 is lithium (Li), which typically forms basic oxides. (c) An element with atomic number 12 is magnesium (Mg), which forms basic oxides. (d) An element with atomic number 19 is potassium (K), which forms basic oxides.Therefore, the element that will form an acidic oxide is: (a) An element with atomic number 7 .]
22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element
Answer : (b) Metalloid
[The element with atomic number 14 is silicon (Si). Silicon is a metalloid. Metalloids exhibit properties that are intermediate between metals and non-metals. In the given options, the correct answer is: (b) Metalloid. ]
23. Which one of the following depict the correct representation of atomic radius(r) of an atom?
(i) (ii) (iii) (iv) Photo
(a) (i) and (ii) (b) (ii) and (iii)
(c) (iii) and (iv) (d) (i) and (iv)
Answer : (b) (ii) and (iii)
24. Which one of the following does not increase while moving down the group of the periodic table?
(a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Answer : (c) Valence
[ Explanation: Moving down a group in the periodic table:
(i) Atomic radius increases due to addition of new electron shells.
(ii) Metallic character increases as atoms lose electrons more easily.
(iii) Number of shells increases with each successive period.
(iv) Valence remains the same because elements in the same group have the same number of valence electrons.
So, the only option that does not increase is valence.]
25. On moving from left to right in a period in the periodic table, the size of the atom.
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Answer : (b) decreases
[ As we move from left to right in a period, the number of protons in the nucleus increases, which increases the nuclear charge. The electrons are added to the same shell, so shielding does not increase much. Due to the stronger attraction between the nucleus and electrons, the atomic size decreases across the period.]
26. Which of the following set of elements is written in order of their increasing metallic character?
(a) Be Mg Ca
(b) Na Li K
(c) Mg Al Si
(d) C O N
Answer : (a) Be Mg Ca
[ The correct set of elements written in order of their increasing metallic character is: (a) Be < Mg < Ca ]
Short Answer Questions
27. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.
Answer : This arrangement of elements is called an arithmetic progression. An example of such a set of elements is lithium (Li), beryllium (Be), and boron (B) with atomic masses in increasing order.
28. Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
F, Na, Mg, Al, Si, P, S, Cl, Ar, K
(a) Pick two sets of elements which have similar properties.
(b) The given sequence represents which law of classification of elements?
Answer : (a) Two sets of elements with similar properties in the given sequence are:
Na (Sodium) and K (Potassium)
Cl (Chlorine) and Br (Bromine)
(b) The given sequence represents Mendeleev's Law of Periodicity .
29. Can the following groups of elements be classified as Dobereiner's triad ?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40
Explain by giving reason.
Answer : Dobereiner's triads are sets of three elements with similar chemical properties and the atomic mass of the middle element being approximately the average of the other two. Let's analyze the given groups:
(a) Na, Si, Cl
Atomic masses: Na (23), Si (28), Cl (35)
Si's atomic mass is not approximately the average of Na and Cl.
Therefore, this group does not form a Dobereiner's triad.
(b) Be, Mg, Ca
Atomic masses: Be (9), Mg (24), Ca (40)
Mg's atomic mass is approximately the average of Be and Ca (24 = (9 + 40)/2).
Therefore, this group can be classified as Dobereiner's triad.
30. In Mendeleev′ ’s Periodic Table the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.
Answer : Mendeleev arranged elements based on their chemical properties rather than strict adherence to atomic masses. Cobalt (Co) was placed before nickel (Ni) because they share similar chemical properties, even though cobalt's atomic mass is slightly greater than nickel's.
31. “Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement.
Answer : Dual Nature: Hydrogen exhibits properties of both metals and nonmetals, making its classification challenging.
Uncertain Grouping: Hydrogen's placement in Group 1 or 17 varies, reflecting its unique position and distinct behavior compared to other elements in these groups.
32. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by ′Mendeleev.
Answer : The elements predicted by Mendeleev as Eka-silicon and Eka-aluminium correspond to germanium (Ge) and gallium (Ga), respectively. The chlorides of these elements are:
Chloride of Eka-silicon (Germanium): ECl₄
Chloride of Eka-aluminium (Gallium): ECl₃
33. Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern Periodic Table. Also, give their valencies.
Answer : The group number in the Modern Periodic Table is determined by the number of electrons in the outermost shell.
Element A with 3 electrons in the outermost shell belongs to Group 13. Its valency is 3.
Element B with 4 electrons in the outermost shell belongs to Group 14. Its valency can vary, but it is commonly 4.
Element C with 2 electrons in the outermost shell belongs to Group 2. Its valency is 2.
34. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?
Answer : The formula of the chloride for an element X in Group 14 is XCl4 , and the nature of bonding is typically covalent.
35. Compare the radii of two species X and Y. Give reasons for your answer.
(a) X has 12 protons and 12 electrons
(b) Y has 12 protons and 10 electrons
Answer : (a) X has 12 protons and 12 electrons:
X is a neutral atom, so the atomic radius is typical.
(b) Y has 12 protons and 10 electrons:
Y is an ion with a 2- charge, making it smaller due to stronger attractive forces pulling electrons closer.
36. Arrange the following elements in increasing order of their atomic radii.
(a) Li, Be, F, N
(b) Cl, At, Br I
Answer :
(a) Increasing order of atomic radii: F < N < Be < Li
(b) Increasing order of atomic radii: Cl>Br>I>At
37. Identify and name the metals out of the following elements whose electronic configurations are given below.
(a) 2, 8, 2
(b) 2, 8, 1
(c) 2, 8, 7
(d) 2, 1
Answer : (a) Metal: Magnesium (Mg) -2.8.2
(b) Metal: Sodium (Na) – 2.8.1
(c) Metal: Chlorine (Cl) – 2.8.7
(d) Metal: Lithium (Li) – 2.1
38. Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the bond formed?
Answer : Atomic number of A = 19
E.C. of A = 2.8.8.1
The valency of A is 1 .
Atomic number of B = 17
E.C. of B = 2.8.7
The valency of B is 1 (= 8 – 7).
Therefore, the formula of the product is AB .
39. Arrange the following elements in the increasing order of their metallic character
Mg, Ca, K, Ge, Ga
Answer : The metallic character generally increases from right to left and from top to bottom in the periodic table. Therefore, the increasing order of metallic character for the given elements is:
Ge < Ga < Mg < Ca < K
40. Identify the elements with the following property and arrange them in increasing order of their reactivity
(a) An element which is a soft and reactive metal
(b) The metal which is an important constituent of limestone
(c) The metal which exists in liquid state at room temperature
Answer : (a) An element which is a soft and reactive metal:
This describes sodium (Na).
(b) The metal which is an important constituent of limestone:
This describes calcium (Ca).
(c) The metal which exists in a liquid state at room temperature:
This describes mercury (Hg).
Arranging them in increasing order of reactivity: Ca<Na<HgCa<Na<Hg
41. Properties of the elements are given below. Where would you locate the following elements in the periodic table?
(a) A soft metal stored under kerosene
(b) An element with variable (more than one) valency stored under water.
(c) An element which is tetravalent and forms the basis of organic chemistry
(d) An element which is an inert gas with atomic number 2
(e) An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “ anodising”.
Answer :(a) A soft metal stored under kerosene:
Sodium (Na) is in Period 3 and Group 1 of the periodic table.
(b) An element with variable valency stored under water:
Phosphorous (P) is in Period 3 and Group 15 of the periodic table.
(c) An element which is tetravalent and forms the basis of organic chemistry:
Carbon (C) is in Period 2 and Group 14 of the periodic table.
(d) An element which is an inert gas with atomic number 2:
Helium (He) is in Period 1 and Group 18 of the periodic table.
(e) An element whose thin oxide layer is used to make other elements corrosion-resistant by the process of "anodizing":
Aluminum (Al) is in Period 3 and Group 13 of the periodic table.
Long Answer Questions
42. An element is placed in 2nd Group and 3rd Period of the Periodic Table, burns in presence of oxygen to form a basic oxide.
(a) Identify the element
(b) Write the electronic configuration
(c) Write the balanced equation when it burns in the presence of air
(d) Write a balanced equation when this oxide is dissolved in water
(e) Draw the electron dot structure for the formation of this oxide
Answer : (a) Element: Magnesium (Mg)
(b) Electronic configuration of Mg is 2.8.2
(c) Balanced equation when it burns in the presence of air:
2Mg+O2→2MgO
(d) Balanced equation when the oxide is dissolved in water:
MgO+H2O→Mg(OH)2
(e) Electron dot structure for the formation of MgO:
Mg⋅+O⋅⋅→MgO
Dot structure
43. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
(a) Where in the periodic table are elements X and Y placed?
(b) Classify X and Y as metal (s), non-metal (s) or metalloid (s)
(c) What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed
(d) Draw the electron dot structure of the divalent halide.
Answer : (a) Elements X and Y are placed in Period 3 and Period 4 of the periodic table, respectively.
(b) Element X (atomic number 17) is a non-metal, likely chlorine (Cl), and Element Y (atomic number 20) is a metal, likely calcium (Ca).
(c) The oxide of element Y (calcium) will be basic in nature. The nature of bonding in the compound formed between X and Y would be ionic.
(d) Electron dot structure of the divalent halide (CaX₂): X⋅:Ca:X⋅X⋅:Ca:X⋅
44. Atomic number of a few elements are given below
10, 20, 7, 14
(a) Identify the elements
(b) Identify the Group number of these elements in the Periodic Table
(c) Identify the Periods of these elements in the Periodic Table
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements
Answer :The details for each element:
(a) Element Identification:
10: Neon (Ne) ; 20: Calcium (Ca) ; 7: Nitrogen (N) ; 14: Silicon (Si)
(b) Group Number:
10 (Ne): Group 18 (Noble Gases)
20 (Ca): Group 2 (Alkaline Earth Metals)
7 (N): Group 15 (Nitrogen Family)
14 (Si): Group 14 (Carbon Family)
(c) Periods:
10 (Ne): Period 2
20 (Ca): Period 4
7 (N): Period 2
14 (Si): Period 3
(d) Electronic Configuration:
10 (Ne): 2.8
20 (Ca): 2.8.8.2
7 (N): 2.5
14 (Si): 2.8.4
(e) Valency:
10 (Ne): 0 (Noble Gases typically have a valency of 0)
20 (Ca): 2
7 (N): 3
14 (Si): 4
45.
46. (a) In this ladder (Figure 5.2) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic number in the Periodic Table.
(b) Arrange them in the order of their group also.
Fig. 5.2
47. Mendeleev′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements
(b) Mention the group and the period of these elements in the Modern Periodic Table.
(c) Classify these elements as metals, non-metals or metalloids
(d) How many valence electrons are present in each one of them?
Answer : (a) The elements that correspond to Mendeleev's predictions are germanium (Ge) for Eka-silicon and gallium (Ga) for Eka-aluminium.
(b) In the Modern Periodic Table:
Germanium (Ge) is in Group 14 and Period 4.
Gallium (Ga) is in Group 13 and Period 4.
(c) Classification:
Germanium (Ge) is a metalloid.
Gallium (Ga) is a metal.
(d) Valence electrons:
Germanium (Ge) has 4 valence electrons.
Gallium (Ga) has 3 valence electrons.
48. (a) Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them
(b) Name the most electronegative element
(c) Name the element with smallest atomic size
(d) Name the element which is a metalloid
(e) Name the element which shows maximum valency.
Answer : (a) The most electropositive element among elements with atomic numbers 3 to 9 is:
Sodium (Na) with atomic number 11.
(b) The most electronegative element among elements with atomic numbers 3 to 9 is:
Fluorine (F) with atomic number 9.
(c) The element with the smallest atomic size among elements with atomic numbers 3 to 9 is:
Lithium (Li) with atomic number 3.
(d) The element which is a metalloid among elements with atomic numbers 3 to 9 is:
Boron (B) with atomic number 5.
(e) The element which shows the maximum valency among elements with atomic numbers 3 to 9 is:
Oxygen (O) with atomic number 8.
49. An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and
are the major air pollutants.
(a) Identify the element X
(b) Write the electronic configuration of X
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?
(d) What would be the nature (acidic/ basic) of oxides formed?
(e) Locate the position of the element in the Modern Periodic Table.
Answer : (a) Element X: Sulphur (S)
(b) Electronic configuration of Sulphur (S) is 2.8.6
(c) Balanced chemical equation for the thermal decomposition of ferrous sulfate crystals: 4FeSO4⋅7H2O→Fe2(SO4)3+Fe2O3+7H2O+SO2↑
(d) Nature of oxides formed: The oxides formed (SO₂ and SO₃) are acidic in nature.
(e) Position in the Modern Periodic Table: Sulfur (S) is located in Group 16 (Chalcogens) and Period 3.
50. An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic
pungent smell.
(a) Identify the element X. How many valence electrons does it have?
(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?
(c) Draw the electron dot structure for ammonia and what type of bond is formed in it?
51. Which group of elements could be placed in Mendeleev's′ Periodic Table without disturbing the original order? Give reason.
52. Give an account of the process adopted by ′Mendeleev for the classification of elements. How did he arrive at “Periodic Law”?
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