Question

Identify the correct statements from the following.
(i) Oxygen shows $-2,-1,+1$ and $+2$ oxidation states.
(ii) The thermal stability of $H _{2} O , H _{2} Se$ and $H _{2} S$ follows the order $H _{2} O < H _{2} S < H _{2} Se$.
(iii) The reducing nature of $H _{2} Se , H _{2} S$ and $H _{2}\, Te$ follows the order $H _{2} S < H _{2} Se < H _{2} Te$

• A. i, ii, iii
• B. i, ii
• C. i, iii
• D. ii, iii

Answer 1

Answer: (C)

Oxygen shows $-2-1,+1$ and $+2$ oxidation states.

(i) Oxygen shows $-2$ oxidation states in most of its compound while it shows $( - 1) O.S.$ in peroxides $($ like $\left.H _{2} O _{2}\right),+1$ in $O _{2} F _{2}$ and $+2$ in $OF _{2}$.

Thus, it show $-2,-1,+1$ and $+2$ oxidation states.

(ii) The thermal stability of $H _{2} O , H _{2} Se$ and $H _{2} S $ follows the order

$H _{2} O > H _{2} S > H _{2} Se$

This is because, on going down the group, the size of the central atom increases and therefore, its tendency to form stable covalent bond with hydrogen decreases. As a result, the $M- H$ bond strength decreases and therefore, thermal stability decreases.

(iii) The reducing nature of $H _{2} Se , H _{2} S$ and $H _{2} Te$ follows the order

$H _{2} S < H _{2} Se < H _{2} Te$

This is due to the decrease in thermal stability of the hydride greater the unstability of hydrides, the greater is its reducing character.