Question

Which of the following statements are correct for alkali metal compounds?
(i) Superoxides are paramagnetic in nature.
(ii) The basic strengths of hydroxides increases down the group.
(iii) The conductivity of chlorides in their aqueous solutions decreases down the group.
(iv) The basic nature of carbonates in aqueous solutions is due to cationic hydrolysis.

• A. (i), (ii) and (iii) only
• B. (i) and (ii) only
• C. (ii), (iii) and (iv) only
• D. (iii) and (iv) only

Answer 1

Answer: (B)

(i) and (ii) only

(i) The alkali metal superoxides contain $O_2^{-}$ ion, which has an unpaired electron, hence they are paramagnetic in nature.

(ii) The basic character of alkali metal hydroxides increases on moving down the group.

(iii) The conductivity of alkali metal chlorides in their aqueous solution increases on moving down the group because in aqueous solution alkali metal chlorides ionise to give alkali metal ions. On moving down the group the size of alkali metal ion increases, thus the degree of hydration decreases, due to this reason their conductivity in aqueous solution increases on moving down the group.

(iv) $M_{2}C{O}_3\begin{array}{c}\text{Ionisation in}\\ \rightleftharpoons \\ \text{aq solution}\end{array}2M^{+}+C{O}_3^{2-}$

${CO}_3^{2-}+2H_{2}O⟶H_{2}C{O}_3+2O{H}^{-}$

Thus, the basic nature of carbonates in aqueous solution is due to anionic hydrolysis.

Hence, the correct option is $\text{B}$