Due to $p\pi - p\pi$ bonding interactions, nitrogen forms $N_2$ but phosphorus forms $X$ and does not form a diatomic molecule. Identify $X$.

When aluminium phosphide is treated with dil. sulphuric acid,which gas is evolved?

Of the following,the most acidic is

The number of $H$ atoms attached to the phosphorus atom in hypophosphorous acid is

Given below are the two statements: one is labeled as Assertion $(A)$ and the other is labeled as Reason $(R)$.
Assertion $(A)$: There is a considerable increase in covalent radius from $N$ to $P$. However,from $As$ to $Bi$,only a small increase in covalent radius is observed.
Reason $(R)$: Covalent and ionic radii in a particular oxidation state increase down the group.
In the light of the above statements,choose the most appropriate answer from the options given below:

What are neutral oxides? Give examples.