Temperature of maximum density of $H_2O$ is $y \ K$ and $D_2O$ is $x \ K$. $(x-y)$ (in $K$) is nearly

The temporary hardness of water is due to

Which of the following hydrides has the lowest boiling point?

The substance used as a universal solvent is .....

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T$.: $Na\underline{H} + H_2O \longrightarrow NaOH + H_2 \uparrow$

What properties of water make it useful as a solvent? What types of compound can it $(i)$ dissolve,and $(ii)$ hydrolyse?