The element which is essential in nitrogen fixation is

The good reducing nature of $H_3PO_2$ is attributed to the presence of:

On heating,compound $(A)$ gives a gas $(B)$ which is a constituent of air. This gas,when treated with $H_{2}$ in the presence of a catalyst,gives another gas $(C)$ which is basic in nature. $(A)$ should not be:

$A$ tetra-atomic molecule $(A)$ on reaction with excess oxygen produces substance $(B)$. $(B)$ is a dehydrating agent. The substances $(A)$ and $(B)$ respectively will be:

The most acidic among the following compounds is

The molecular formula of an acid of phosphorus is $H_3PO_2$. What are its name and basicity,respectively?