Question

With reference to protonic acids, which of the following statements is correct?
(A) $P{H_3}$ is more basic than $N{H_3}$
(B) $P{H_3}$ is less basic than $N{H_3}$
(C) $P{H_3}$ is equally basic than $N{H_3}$
(D) $P{H_3}$ is amphoteric while $N{H_3}$ is basic
(E) None of the above

Answer 1

Protonic acids are those acids that form positive hydrogen ions ($H{}^ +$) in their aqueous solution. This term “Protonic acid” is used to differentiate between ‘traditional’ acids from Lewis acids or Lowry-Brønsted acids in the non-aqueous solvents.

Complete answer:
$P{H_3}$ or phosphine is a highly inflammable and toxic gas with a rotten fish smell while $N{H_3}$is an inorganic compound of nitrogen and hydrogen that is found in air, soil, and water present in the atmosphere.
$P{H_3}$ and $N{H_3}$both are hydrides of Hydrogen and act as a lewis base due to the presence of lone pairs of electrons on $P$ and $N$.
$P{H_3}$ is less basic as compared to $N{H_3}$ ​. The hydrides of group $15$ show basic character due to the presence of a lone pair of electrons. Ammonia is more basic because it can easily donate its lone pair of electrons due to the small size of nitrogen.
As the electron density of the lone pair is concentrated over a small region in nitrogen, $N{H_3}$ can attract the proton much easily in the aqueous solution. ​$P{H_3}$ is a weak base because of the large size of the P atom. As the electron density around P gets scattered over a large region, its ability to attract protons decreases.
Hence, $P{H_3}$ is less basic than $N{H_3}$

Therefore, option (B) is correct.
Note:
In group $15$ the basic character decreases from $N{H_3}$ to $Bi{H_3}$. Between $N{H_3}$ and $P{H_3}$ $N{H_3}$ has a more basic character due to its small size and its ability to donate the lone pair of electrons. $N{H_3}$ is a colorless gas with a very pungent smell.