When $PbO_2$ reacts with conc. $HNO_3$,the gas evolved is:

Given below are two statements:
Statement-$I$: Element '$X$' and '$Y$' are the most and least electronegative elements, respectively, among $N, As, Sb$ and $P$. The nature of the oxides $X_{2}O_{3}$ and $Y_{2}O_{3}$ is acidic and amphoteric, respectively.
Statement-$II$: $BCl_{3}$ is covalent in nature and gets hydrolysed in water. It produces $[B(OH)_{4}]^{-}$ and $HCl$ in aqueous medium.

Taking stability as the factor,which one of the following represents the correct relationship?

The important method for the fixation of nitrogen is

Which of the following exhibits the highest solubility in water?

What is the similarity between $NH_3$ and $PH_3$?