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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3qc219

Which statements about the Nessler's test for $NH X_{4} X^{+}$ are correct?

Athe reagent must be strongly alkaline
Bmercury is in +2 state in both the reagent and the brown product
Cnitrogen is in the $- 3$ oxidation state in the amido group of the brown product
Dthe reagent $K X_{2} [HgI X_{4}]$ contains Hg in the +4 state

Answer: A, B, C

The test needs

OH X^{-}

to free ammonia. Hg is +2 in

[HgI X_{4}] X^{2 -}

(charge

x - 4 = - 2

) and also in

HgO \cdot Hg (NH X_{2}) I

(no redox change); N in

NH X_{2} X^{-}

is

- 3

, since H is +1. A +4 state for Hg is wrong.

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