​$$\text{The rate of hydration of } [\text{Cr}^{\text{III}}(\text{H}_2\text{O})_5X]^{n+} \, (\text{X = N}_3^-, \, \text{F}^-, \, \text{CN}^-, \text{ and NH}_3) \text{ in neutral aqueous medium} \\\text{remains unaffected in acidic medium at room temperature, if ‘X’ is}$$​​

Correct option is D

The rate of hydration of the chromium(III) complex [Cr^III(H₂O)₅X]ⁿ⁺ depends on the ligand X, which influences how the complex reacts in different environments. In acidic medium, certain ligands will have less impact on the rate of hydration compared to others.

​Ammonia (NH₃) is a neutral ligand and does not affect the hydration rate significantly in either neutral or acidic environments. This is because NH₃ does not undergo protonation in acidic medium under normal conditions at room temperature, unlike other ligands such as cyanide or fluoride that may interact differently in acidic solutions. The neutral nature of NH₃ allows it to remain relatively unaffected in acidic environments, thus keeping the rate of hydration unchanged. This makes NH₃ the correct choice, as it does not interfere with the hydration process in acidic medium, unlike the other anionic ligands.

Additional Knowledge

​N₃^- (Azide ion): The azide ion is a relatively weak field ligand. In acidic solutions, azide can undergo protonation to form HN₃ (hydrazoic acid), which can change the ligand's properties and potentially alter the hydration rate of the complex. The protonation of azide under acidic conditions can affect its interaction with the metal center, potentially changing the rate of hydration.

F^- (Fluoride): Fluoride ions (F^-) can form strong hydrogen bonds with water molecules, which could influence the hydration process. In acidic media, fluoride is known to be more reactive and could interact with protons, which may change the hydration rate. The fluoride ion’s behavior in acidic medium is different from that of ammonia, which is why the hydration rate could be affected by fluoride.

CN^- (Cyanide): Cyanide (CN^-) is a strong field ligand and can form stable complexes with transition metals like Cr(III). Cyanide’s strong field character and its ability to act as a ligand with Cr(III) make the complex highly stable. However, in acidic media, cyanide can dissociate and form HCN (hydrogen cyanide), which changes its nature and can impact the hydration rate, unlike ammonia, which remains unaffected.

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