COMEDK · Chemistry · 10. Hydrogen

Arrange the hydrides of group 15 in correct decreasing order of reducing nature.

A \(\mathrm{NH}_{3} < \mathrm{PH}_{3} < \mathrm{AsH}_{3} < \mathrm{SbH}_{3} < \mathrm{BiH}_{3}\)
B \(\mathrm{NH}_{3}>\mathrm{PH}_{3}>\mathrm{AsH}_{3}>\mathrm{SbH}_{3}>\mathrm{BiH}_{3}\)
C \(\mathrm{PH}_{3} < \mathrm{AsH}_{3} < \mathrm{SbH}_{3} < \mathrm{BiH}_{3} < \mathrm{NH}_{3}\)
D \(\mathrm{BiH}_{3}>\mathrm{SbH}_{3}>\mathrm{AsH}_{3}>\mathrm{PH}_{3}>\mathrm{NH}_{3}\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\mathrm{BiH}_{3}>\mathrm{SbH}_{3}>\mathrm{AsH}_{3}>\mathrm{PH}_{3}>\mathrm{NH}_{3}\)

Step-by-step Solution

Detailed explanation

Trihydrides of group 15 elements are given on the basis of reducing character as follows: \[ \mathrm{BiH}_{3}>\mathrm{SbH}_{3}>\mathrm{AsH}_{3}>\mathrm{PH}_{3}>\mathrm{NH}_{3} \] The reducing character increases down the group because the bond strength of \(E-H\) bond decreases.…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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