Railway Science (Chemistry-Structure of Atom) (Part-II)

Total Questions: 50

1. What is the atomicity of phosphorus? [RRB Group D 09/10/2018 (Afternoon)]

Correct Answer: (b) 4
Solution:

Phosphorus (symbol ‘P’, atomic number- 15): The formula of one molecule of phosphorus is P₄ . This indicates that one molecule of phosphorus consists of four phosphorus atoms bonded together. Atomicity refers to the number of atoms present in a single molecule of a substance.

2. Which of the following atoms is polyatomic? [RRB Group D 10/10/2018 (Morning)]

Correct Answer: (d) sulfur
Solution:

Polyatomic elements: These elements exist as molecules containing two or more atoms of the same element bound together. Examples of polyatomic elements include Selenium (Se₈),and Ozone (O₃). Chlorine (Cl₂) - Diatomic molecules. Argon (Ar) - Single atom.

3. Neutrons are present in all atoms except ______:. [RRB Group D 10/10/2018 (Evening)]

Correct Answer: (b) H
Solution:

Neutrons are present in the nucleus of all atoms, except hydrogen. In general, a neutron is represented as ‘n’. The mass of an atom is therefore given by the sum of the masses of protons and neutrons present in the nucleus.

4. One way of dating fossils is by detecting the ratio of different _______ of the same element in the fossil material. [RRB Group D 11/10/2018 (Morning)]

Correct Answer: (b) isotopes
Solution:

The atoms of the same element, having the same atomic number but different mass number. Example - Protium, Deuterium, and Tritium. Allotropes - The atoms of the element are bonded together in different manners. Example - Diamond and Graphite are the allotropes of carbon. Isobars - Two Elements have the same mass numbers but different atomic numbers. Example - Potassium (⁴⁰K₁₉), and calcium (⁴⁰Ca₂₀). Isomers - A molecule with the same molecular formula as another molecule, but with a different chemical structure. Example - Pentane and Isopentane.

5. What is the valence power (potential) of an element called ? [RRB Group D 11/10/2018 (Afternoon)]

Correct Answer: (d) Valency
Solution:

Atomicity: This refers to the number of atoms in a molecule of an element. Atomic mass: This represents the average mass of an element's atoms. Normality: It is equal to molarity multiplied by the number of equivalents in the formula unit of the solute.

6. An electron has a negative charge: [RRB Group D 16/10/2018 (Afternoon)]

Correct Answer: (d) 1.6 × 10⁻¹⁹ C⁻¹
Solution:

Electrons were invented by J. J. Thomson who was a Nobel Prize winner in Physics in 1897. 6.25 × 10¹⁸ electrons taken together make one coulomb.

7. Which of the following elements has the largest ions ? [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (b) Na
Solution:

The removal of an electron from an atom results in the formation of a cation, whereas gain of an electron leads to an anion. The ionic radii can be estimated by measuring the distances between cations and anions in ionic crystals.

8. What is the smallest possible unit of a compound is called ? [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (a) Molecule
Solution:

Molecule is an aggregate of two or more than two atoms of the same or different elements in a definite arrangement. Atom is the smallest particle of an element that retains its (elements) chemical properties. Nucleus is a positively charged region at the center of the atom.

9. _______ does NOT exhibit the periodicity in properties of the elements. [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (d) 𝑁/𝑃 ratio
Solution:

The ratio of the number of neutrons to that of the number of protons. Atomic size is the distance between the center of the nucleus and the outermost shell of an isolated atom. It is also known as atomic radius. Electron affinity is the ability of an atom to accept an electron.

10. Covalently bonded molecules have low melting and boiling points because: [RRB Group D 22/10/2018 (Afternoon)]

Correct Answer: (d) Intermolecular forces are weak
Solution:

A covalent bond is when atoms share electrons to form pairs, called shared or bonding pairs, creating a stable balance of attractive and repulsive forces known as covalent bonding.