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When excess of aq. HNO3 is added to [Cr(H2O)6]2+, it produces [(Cr(H2O)6)]3+.

1. Following equilibrium exist in the given aqueous solution [Cu(H2O)4]2+ (aq) + 4NH3 (aq) ⇌ [Cu(NH3)4]2+ (aq) + 4H2O (l)
2. When HNO3 is added to this solution: (excess) HNO3 (aq) + NH3 (aq) → NH4+ (aq) + NO3− (aq)
3. Thus, amount of NH3 (aq) will reduce drastically. With a simple application of Le Chatelier's principle, the equilibrium will shift towards left in the first reaction. Hence, [(Cu(H2O)4)]2+ will form.
4. None of the above

Correct answer: When HNO3 is added to this solution: (excess) HNO3 (aq) + NH3 (aq) → NH4+ (aq) + NO3− (aq)

Solution

When excess HNO3 is added, it reacts with NH3 to form NH4+ and NO3−. This reduces the concentration of NH3, causing the equilibrium to shift left as per Le Chatelier's principle, favoring the formation of [Cu(H2O)4]2+.

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