Define the term 'valency'. With reference to water & ammonia as compounds respectively state the valency of oxygen & nitrogen. Magnesium [2, 8, 2] has valency 2⁺. Give reasons.

Explain the term 'variable valency'. Copper having electronic configuration 2, 8, 18, 1 exhibits variable valency. Give a reason for the same & name the compound CuCl & CuCl₂.

Certain metals exhibit variable valencies which include valencies: 1⁺, 2⁺, 3⁺, & 4⁺. State the variable valency of the following metals -

(a) Copper

(b) Silver

(c) Mercury

(d) Iron

(e) Tin

(f) Lead

[write each symbol with the variable valency]

State which of the following ions or radicals given below of non-metallic elements exhibit valency: 1^-, 2^- & 3^-

(a) Chloride

(b) Bromide

(c) Iodide

(d) Nitrate

(e) Hydroxide

(f) Bicarbonate

(g) Bisulphite

(h) Bisulphate

(i) Aluminate

(j) Permanganate

(k) Oxide

(l) Sulphide

(m) Sulphite

(n) Sulphate

(o) Carbonate

(p) Dichromate

(q) Zincate

(r) Plumbite

(s) Phosphate

(t) Nitride

[write each ion or radical with the correct valency]