Which of the following will be dissolved in excess of $NaOH$?

$A + H_2O \to NaOH$; $A$ $\xrightarrow[400 \ ^oC]{O_2} B$ $\xrightarrow[25 \ ^oC]{H_2O} NaOH + O_2$
$B$ is used for oxygenating in submarines. $A$ and $B$ are:

The reaction of water with sodium and potassium is

The stability of peroxides and superoxides of alkali metals increases as we go down the group. Explain giving reasons.

Which of the following properties is $NOT$ correct for alkali metals?

Give the biological importance of the sodium ion $(Na^+)$.