Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R) .$
Assertion $(A) :$ ${PH}_{3}$ has lower boiling point than ${NH}_{3} .$
Reason $(R) :$ In liquid state ${NH}_{3}$ molecules are associated through Vander Waal's forces, but ${PH}_{3}$ molecules are associated through hydrogen bonding.
In the light of the above statements, choose the most appropriate answer from the options given below:

Question

Given below are two statements: one is labelled as Assertion

(A)

and the other is labelled as Reason

(R) .

Assertion

(A) :

{PH}_{3}

has lower boiling point than

{NH}_{3} .

Reason

(R) :

In liquid state

{NH}_{3}

molecules are associated through Vander Waal's forces, but

{PH}_{3}

molecules are associated through hydrogen bonding.

In the light of the above statements, choose the most appropriate answer from the options given below:

Aicharya · Accepted Answer

The molecular formulas for ammonia and phosphine are ${NH}_{3}$ and ${PH}_{3}$
, respectively. As we know, Nitrogen is more electronegative and smaller in size than phosphorus. Therefore, hydrogen bonding occurs in ammonia in comparison to phosphine. Hydrogen bonding is the force of attraction between hydrogen and an electronegative element which is smaller in size. In the case of phosphine, only weak van der waal’s forces of attraction exist between the molecules. Since hydrogen bonding is stronger than weak van der waal’s forces of attraction. Hence, ammonia has a higher boiling point than phosphine.
In all, we can say that hydrogen bonding is responsible for the higher boiling point of ammonia in comparison to phosphine.

$N$ has small atomic size and high electronegativity. Hence, ${NH}_{3}$ can form hydrogen bonds. $P$ has large size and low electronegativity. Hence, ${PH}_{3}$ cannot form hydrogen bonds.

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R .…

Solution