Define or explain the following terms :

(i) Absolute temperature

(ii) Valency

(iii) Ozone depletion

(iv) Electrovalent bond

(v) Atom

(i) Absolute temperature — The temperature on the Kelvin scale at which molecular motion completely ceases is called absolute zero. Absolute zero is -273°C.

(ii) Valency — Valency is the combining capacity of an atom of an element or of a radical with the atoms of other elements or radicals to form molecules.

(iii) Ozone depletion — Ozone layer depletion is the thinning of the ozone layer present in the upper atmosphere. This happens when the chlorine and bromine atoms in the atmosphere come in contact with ozone and destroy the ozone molecules

(iv) Electrovalent bond — The chemical bond formed between two atoms by transfer of one or more electrons from the atom of a metallic (electropositive) element to an atom of a non-metallic (electronegative) element is called ionic bond or electrovalent bond.

(v) Atom — An atom is the smallest particle of an element that exhibits all the properties of that element. It may or may not exist independently but takes part in every chemical reactions.