Q.(a)

Isotopes of hydrogen -- protium, deuterium, tritium -- differ only in neutron number; calcium finds wide use in metallurgy, construction, and industry. (This answers part (a) of the OR question.)

(i) Isotopes:

Isotopes are atoms of the same element that have the same atomic number (same number of protons, and hence the same number of electrons and identical chemical properties) but different mass numbers, because they contain different numbers of neutrons in the nucleus.

Hydrogen has three well-known isotopes:

1. Protium (1H or H): mass number 1, contains 1 proton and 0 neutrons. This is the most abundant (about 99.98%) form of hydrogen.
2. Deuterium (2H or D): mass number 2, contains 1 proton and 1 neutron. Present in trace amounts (about 0.015%); its oxide is heavy water (D2O).
3. Tritium (3H or T): mass number 3, contains 1 proton and 2 neutrons. It is radioactive (beta emitter) and occurs only in very minute traces in nature (produced continuously in the upper atmosphere by cosmic-ray reactions, and also made artificially).

(ii) Uses of Calcium:

• Calcium metal is used as a reducing agent in the extraction of metals such as thorium, uranium, and zirconium from their compounds (metallothermic reduction).
• Used as a deoxidiser and desulfuriser in the manufacture of steel and other alloys, and to remove air/gas traces from vacuum tubes (getter).
• Used in making useful alloys, such as calcium-lead alloys for battery grids. …