Which of the following drying agents reacts with $CO_2$ and also removes moisture?

Among the following,the correctly matched pair is

Name the classes of hydrides to which $H_2O$,$B_2H_6$ and $NaH$ belong.

Which compound is formed on catalytic hydrogenation of carbon monoxide at high $p$ and high $T$ in the presence of $ZnO-Cr_2O_3$ catalyst?

Non-stoichiometric hydrides are formed by

Hydrogen iodide cannot be prepared by the action of concentrated $H_2SO_4$ on potassium iodide because: