Chemistry

Total Questions: 69

51. Which of the following statements is NOT true about compounds? [S.S.C. Online CHSL (T-I) 14.10.2020]

(a) Compounds have a variable composition
(b) The constituents can be separated only by chemical or electrochemical reactions.
(c) Elements react to form new compounds.
(d) The composition of each new substance is always fixed.

Correct Answer: (a) Compounds have a variable composition

Solution:The formation of compounds follows the law of constant proportion. That is, whether the compound is obtained from any source or made by any method, its constituent elements always combine in a certain proportion. For example, the mass of hydrogen and oxygen in water (H₂O) is always 1: 8.

52. Why do atoms bond? [S.S.C. Online CHSL (T-I) 22.01.2017]

(a) To reduce potential energy and gain stability
(b) To make atoms
(c) To increase potential energy and lose stability
(d) To increase potential energy and gain stability

Correct Answer: (a) To reduce potential energy and gain stability

Solution:Except for the noble gases, most of the elements orbitals are unsaturated with electrons, i.e. the atoms of the elements are not in a state of stable electronic configuration. Thus, atoms combine to form bonds, acquiring stable electronic configuration and attaining stability, and their potential energy decreases.

53. Which of the following is not an element? [S.S.C. Online MTS (T-I) 20.09.2017]

(a) Sodium
(b) Tin
(c) Water
(d) Carbon

Correct Answer: (c) Water

Solution:Elements are those which are made up of the same type of atoms. Therefore, sodium (Na), tin (Sn) and carbon (C) are elements, whereas water is made up of two different elements hydrogen and oxygen. Hence water is a compound. Its chemical formula is H₂O.

54. The number of protons in a Lithium nucleus is: [S.S.C. JE Electrical Exam 24.03.2021]

(a) Four
(b) One
(c) Two
(d) Three

Correct Answer: (d) Three

Solution:The atomic number of Lithium (Li) is 3. Therefore, the number of protons in a lithium nucleus is 3 (three) and its atomic mass is 7 (seven). Lithium is a strong reducing agent. Its melting point and boiling point are higher than other alkali metals. It is currently used in the manufacture of mobile batteries.

55. How many protons are there in a lithium nucleus? [S.S.C. Online CGL (T-I) 18.04.2022]

(a) 2
(b) 4
(c) 5
(d) 3

Correct Answer: (d) 3

Solution:The number of protons in the nucleus of lithium is 3. It is the lightest metal. Lithium is mainly found in Salt and Minerals and used in battery industries.

Symbol: Li
Atomic Number: 3
Group: 1
Period: 2
Block: S
Electronic configuration: [He] 2s¹.

56. What is the atomic weight of Lithium? [S.S.C. Online CHSL (T-I) 19.03.2020]

(a) 9.012 amu, g/mol
(b) 6.941 amu, g/mol
(c) 10.811 amu, g/mol
(d) 4.003 amu, g/mol

Correct Answer: (b) 6.941 amu, g/mol

Solution:The atomic mass of lithium (Li) is 6.941 amu or 6.941 g/mol. Lithium is a member of the alkaline metals group (the first group of the periodic table). The atomic number of lithium is 3.
Symbol: Li
Atomic Number: 3
Group: 1
Period: 2
Block: S
Electronic configuration: [He] 2s¹.

57. Which of the following elements has the largest atomic radii? [S.S.C. Online MTS (T-I) 06.07.2022]

(a) Beryllium
(b) Lithium
(c) Nitrogen
(d) Carbon

Correct Answer: (b) Lithium

Solution:The atomic radius of an element depends on its atomic number and the number of electron shells or energy levels. As we move down group in the periodic table, the number of electron shells increases, and as we move from right to left in a period, the atomic number decreases, resulting in an increase in atomic radius.

Therefore, the element with the largest atomic radius will be found in the lower left-hand corner of the periodic table. Based on the given option, the element with the largest atomic radius is Lithium (Li).

(A) Beryllium (112pm)
(B) Lithium (152pm)
(C) Nitrogen (65pm)
(D) Carbon (70pm)

58. What is the atomic mass of oxygen (expressed in 'u')? [S.S.C. Online CGL (T-I) 18.04.2022]

(a) 24
(b) 8
(c) 16
(d) 32

Correct Answer: (c) 16

Solution:

The atomic mass of oxygen is approximately 16 u (atomic mass units).

The most abundant isotope of oxygen is Oxygen-16 (¹⁶

O

), which has 8 protons and 8 neutrons. Its atomic mass is very close to 16 u. The 'u' stands for unified atomic mass unit, which is a standard unit used for expressing the mass of atoms and molecules.

59. What is the relative density of silver? [S.S.C. Online CHSL (T-I) 19.03.2020]

(a) 7.2
(b) 9.5
(c) 10.4
(d) 10.8

Correct Answer: (d) 10.8

Solution:Relative density can be calculated directly by measuring the density of the sample and dividing it by the (known) density of the reference substance. On this basis, the relative density of silver is estimated to be 10.8.

60. What is the atomic number of chromium? [S.S.C. Online MTS (T-I) 08.07.2022]

(a) 24
(b) 18
(c) 21
(d) 19

Correct Answer: (a) 24

Solution:The atomic number of chromium is 24. Its electronic configuration in ground state 1s²2s²2p⁶3s²3p⁶ 3d⁵4s¹.

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