Which pair of metals dissolves in $NaOH$ solution?

Which of the following statements are correct for alkali metal compounds?
$(i)$ Superoxides are paramagnetic in nature.
(ii) The basic strengths of hydroxides increase 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.

Magnesium liberates $H_2$ gas on reaction with

Soda ash is

Explain the biological importance of sodium and potassium.

$H_2$ gas is not produced in which of the following reactions?