JEE Main · 2022 · 27 Jun 2022 · Shift 2 · s-Block Elements

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BeO reacts with HF in presence of ammonia to give [A] which on thermal decomposition produces [B] and ammonium fluoride. Oxidation state of Be in [A] is ____

Answer: 2

Solution

BeO reacts with HF in the presence of ammonia to form ammonium fluoroberyllate:

BeO + 2HF + 2NH₃ → (NH₄)₂[BeF₄] [A]

On thermal decomposition:
(NH₄)₂[BeF₄] → BeF₂ [B] + 2NH₄F

In compound [A], which is (NH₄)₂[BeF₄], beryllium is in the [BeF₄]²⁻ complex ion. Since fluorine has oxidation state -1, and the overall charge is -2:

Let oxidation state of Be = x
x + 4(-1) = -2
x = +2

Answer: 2

JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Integer answer

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