Strong reducing behaviour of $H_3PO_2$ is due to

When copper metal is treated with cold and dilute nitric acid, it forms

Nitrogen forms how many oxides?

$(NH_4)_2Cr_2O_7$ on heating gives:

The species formed on fluorination of phosphorus pentachloride in a polar organic solvent are

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: