(i) (a) 2O = 2 atoms of oxygen

(b) O_{2} = Diatomic oxygen

(c) O_{3} = Triatomic oxygen / ozone

(d) H_{2}O=Two atoms of hydrogen and one atom of oxygen construct one molecule of water (H_{2}O)

(ii) Potassium carbonate - K_{2}CO_{3 }

Calcium chloride - CaCl_{2 }

(iii) Formula unit mass of any compound is the sum of atomic masses of all atoms in the formula of that compound.

Formula unit mass of Al_{2}(SO_{4})_{3}

Atomic mass of Al = 27 × 2 = 54 u

Atomic mass of S = 32 × 3 = 96 u

Atomic mass of O = 16 × 12 = 192 u

Formula unit mass = 54 + 96 + 192 = 342 u.

Hence, Formula unit mass of Al_{2}(SO_{4})_{3} is 342.