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 $H_2{O}_2),+1$ in $O_2{F}_2$ and $+2$ in $O{F}_2$.

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.