IIT-JEE 2012 · Paper 2 · Chemistry Q23

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ChemistrySingle correct+3 / -1Question 23 of 60

The reaction of white phosphorus with aqueous NaOH gives phosphine along with another phosphorus containing compound. The reaction type; the oxidation states of phosphorus in phosphine and the other product are respectively

redox reaction; −3 and −5

redox reaction; +3 and +5

disproportionation reaction; −3 and +5

disproportionation reaction; −3 and +3

Answer and worked solution

Official answer: Dropped: full marks to everyone

This question was dropped in the official key (marks to all). Below is the standard working, which shows why no option is right.

Reaction.
$\ce{P4 + 3NaOH + 3H2O -> PH3 + 3NaH2PO2}.$
Phosphorus (0) goes to −3 in $\ce{PH3}$ and to +1 in sodium hypophosphite: a disproportionation.

Options. (C) and (D) name the reaction type correctly, but give +5 or +3 for the second product; the correct value is +1. (A) and (B) give impossible states for phosphine. No option matches.

Answer: none of the options (dropped)

Topics:Group 15 Oxidation number

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IIT-JEE 2012 · Paper 2, Chemistry question 23