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 :

(A) is correct but (R) is not correct

Both (A) and (R) are correct and (R) is the correct explanation of (A)

(A) is not correct but (R) is correct

Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Chemical Bonding and Molecular Structure PYQ — JEE Main 2024 · 1 Feb · Shift 1 · Q14 with Solution

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Correct answer: C

Examine the Assertion (A):
Assertion: $\mathrm{PH}_3$ has lower boiling point than $\mathrm{NH}_3$ .
- $\mathrm{NH}_3$ molecules show hydrogen bonding because nitrogen is highly electronegative and bonded to hydrogen.
- $\mathrm{PH}_3$ does not show significant hydrogen bonding because phosphorus is much less electronegative.
- Therefore, intermolecular forces in $\mathrm{NH}_3$ are stronger than in $\mathrm{PH}_3$ .
- Stronger intermolecular forces lead to a higher boiling point.
Hence, $\text{boiling point of } \mathrm{NH}_3 > \text{boiling point of } \mathrm{PH}_3$ so the assertion is correct.
Examine the Reason (R):
Reason: In liquid state $\mathrm{NH}_3$ molecules are associated through van der Waals' forces, but $\mathrm{PH}_3$ molecules are associated through hydrogen bonding.

This is reversed and therefore incorrect.

Correct situation:
- $\mathrm{NH}_3$ molecules are associated through hydrogen bonding.
- $\mathrm{PH}_3$ molecules are mainly associated through weak van der Waals' forces.
Therefore, the reason is not correct.
Conclusion:
- Assertion (A) is correct.
- Reason (R) is not correct.
Therefore, the correct option is: $\boxed{\text{C}}$

View written solutionFree

Correct answer: C

Examine the Assertion (A):
Assertion: $\mathrm{PH}_3$ has lower boiling point than $\mathrm{NH}_3$ .
- $\mathrm{NH}_3$ molecules show hydrogen bonding because nitrogen is highly electronegative and bonded to hydrogen.
- $\mathrm{PH}_3$ does not show significant hydrogen bonding because phosphorus is much less electronegative.
- Therefore, intermolecular forces in $\mathrm{NH}_3$ are stronger than in $\mathrm{PH}_3$ .
- Stronger intermolecular forces lead to a higher boiling point.
Hence, $\text{boiling point of } \mathrm{NH}_3 > \text{boiling point of } \mathrm{PH}_3$ so the assertion is correct.
Examine the Reason (R):
Reason: In liquid state $\mathrm{NH}_3$ molecules are associated through van der Waals' forces, but $\mathrm{PH}_3$ molecules are associated through hydrogen bonding.

This is reversed and therefore incorrect.

Correct situation:
- $\mathrm{NH}_3$ molecules are associated through hydrogen bonding.
- $\mathrm{PH}_3$ molecules are mainly associated through weak van der Waals' forces.
Therefore, the reason is not correct.
Conclusion:
- Assertion (A) is correct.
- Reason (R) is not correct.
Therefore, the correct option is: $\boxed{\text{C}}$