Which of the following has maximum solubility in water?

The correct order of degree of hydration of $M^{+}$ ions of alkali metals is

$A$ $s$-block element $(M)$ reacts with oxygen to form an oxide of the formula $MO_{2}$. The oxide is pale yellow in colour and paramagnetic. The element $(M)$ is:

The total number of elements among $S$,$P$,$Zn$,$Al$,$Sn$,$Pb$ which produce $H_2$ gas with $NaOH$ is

$NaOH$ is prepared by which of the following methods?

Which of the following reactions is not correct?