Railway Science (Chemistry-Structure of Atom)

Total Questions: 50

41. The shape of the path of a free electron in a metal is: [RRB Group D 25/09/2018 (Afternoon)]

Correct Answer: (c) Zig-zag
Solution:

Due to mutual collisions, the molecules of a fluid also move on zig-zag paths. The average distance between two successive collisions of the molecules is called the mean free path.

42. Atomic radius is measured in : [RRB Group D 27/09/2018 (Morning)]

Correct Answer: (b) Nanometres
Solution:

Atomic radius: The measure of the size of the atoms of any element. It is the distance from the center of the nucleus to the outermost shell containing electrons of an element. Radius of nucleus (R ) = 1.2 × 10⁻¹⁵ m = 1.2 fermi-meter. Units: Micron (10⁻⁶m), Nanometer (10⁻⁹m), Fermi (10⁻¹⁵m), Angstrom (10⁻¹⁰m).

43. _________ number of electrons participate in forming bonds in N₂. [RRB Group D 28/09/2018 (Evening)]

Correct Answer: (d) 6
Solution:

There are 3 bonds (one sigma and two pi-bonds) present in nitrogen molecule. A bond is formed by the sharing of two electrons. Hence, for 3 bonds, we require 6 electrons.

44. Which of the following statements is correct according to Dalton's method? [RRB Group D 01/10/2018 (Morning)]

Correct Answer: (d) Atoms are indivisible particles of substances.
Solution:

Atoms of the same elements are similar in shape and mass but differ from the atoms of other elements. Atoms cannot be created or destroyed. Atoms of different elements may combine with each other in fixed, simple, whole-number ratios to form elements and compounds. The atom is the smallest unit of matter that can take part in a chemical reaction.

45. The bonds formed by the elements having larger atoms are: [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (c) very weak
Solution:

Ionic bonds are generated by the complete transfer of valence electrons to achieve stability. Hydrogen Bond - The attractive force that binds one molecule’s hydrogen atom with the electronegative atoms like fluorine, oxygen, and nitrogen of another molecule. Covalent Bonds - Formed between two atoms that share a pair of electrons. Metallic Bond - force that holds atoms together in a metallic substance.

46. If the electronic configuration of an element is 2, 8, 7, then what will be its valency? [RRB Group D 04/10/2018 (Afternoon)]

Correct Answer: (b) 1
Solution:

The number of bonds that an atom can form as part of a compound is expressed by the valency of the element. In this, since the outer shell contains 7 electrons, it requires 1 more electron to reach the stable state.

47. The electronic configuration of an element is 2,8,3. It belongs to ________group. [RRB Group D 08/10/2018 (Morning)]

Correct Answer: (b) 13
Solution:

Aluminum is a chemical element with symbol Al and atomic number 13, which belongs to period 3. Classified as a post-transition metal, aluminum is a solid at room temperature. Its electronic configuration is [Ne] 3s²3p¹ .

48. _________ is the smallest particle of matter which has independent existence. [RRB Group D 08/10/2018 (Morning)]

Correct Answer: (d) molecule
Solution:

Molecules are formed when two or more atoms chemically bond together. Noble gases like helium and neon exist as single atoms because they don't readily bond with other atoms, making them monoatomic and capable of independent existence.

49. _____ atoms are present in sodium carbonate molecules. [RRB Group D 09/10/2018 (Morning)]

Correct Answer: (b) 6
Solution:

Sodium Carbonate (Na₂CO₃) also known as Washing Soda contains 2 sodium atoms, 3 oxygen atoms and one carbon atom. Total number of atoms is 6. It is used in the manufacture of detergents, soaps, and paper. Sodium bicarbonate (NaHCO₃) also known as baking soda.

50. The maximum number of bonds between two atoms of covalent bond can be _________. [RRB Group D 09/10/2018 (Morning)]

Correct Answer: (a) 3
Solution:

Covalent bond is a bond formed between two same or different atoms by mutual contribution and sharing of electrons. Types: Single Covalent bond Hydrogen (H₂), Double Covalent bond Oxygen (O₂), Triple Covalent bond Nitrogen (N₂). Co-ordinate bond (Dative bond) a type of alternate covalent bond that is formed by sharing of an electron pair from a single atom. Example: Ammonium (NH₄⁺) ion, Hydronium ion (H₃O⁺).