JEE Advanced · Chemistry · 21. p Block (G15-18)

Paragraph:
There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridisation easily explains the ease of sigma donation capability of \(\mathrm{NH}_3\) and \(\mathrm{PH}_3\). Phosphine is a flammable gas and is prepared from white phosphorus.
Question:
White phosphorus on reaction with \(\mathrm{NaOH}\) gives \(\mathrm{PH}_3\) as one of the products. This is a

A dimerisation reaction
B disproportionation reaction
C condensation reaction
D precipitation reaction

Verified Solution

Answer & Solution

Correct Answer

(B) disproportionation reaction

Step-by-step Solution

Detailed explanation

White phosphorus on reaction with \(\mathrm{NaOH}\) gives \(\mathrm{PH}_3\) as one of the product in disproportionation reaction
\(
\mathrm{P}_4+3 \mathrm{NaOH}+3 \mathrm{H}_2 \mathrm{O} \longrightarrow 3 \mathrm{NaH}_2 \mathrm{PO}_2+\mathrm{PH}_3
\)

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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