An element M forms the compound $M{ H }_{ 3 }$ when it reacts with hydrogen.
(i) Find the valency of element M.
(ii) Write the valency of chlorine and sulphur.
(iii) Name three isotopes of hydrogen.
(i) Valency of M = 3 because it combines with three atoms of hydrogen.
(ii) Valency of chlorine, Cl (2, 8, 7) = 8 - 7 = 1
Valency of sulphur, S (2, 8, 6) =8 — 6 = 2
(iii) Protium ${H}{1}^{1}$, deuterium ${H}{1}^{2}$ and tritium ${H}_{1}^{3}$.