JEE Chemistry 2025 Question with Solution

Given: The first transition series metal $M$ has the highest enthalpy of atomisation in its series, and one of its aquated ions is green in colour.

Find: The nature of the oxide formed by the corresponding ion.

From the provided solution, the relevant idea is that transition metals in lower oxidation states such as $+2$ generally form basic oxides.

The solution identifies the green aquated ion as a lower oxidation state transition-metal ion and states that the corresponding oxide in that lower oxidation state is basic in nature.

Therefore, the oxide formed is basic.

The correct option is C.

Given: A first transition series metal $M$ has the highest enthalpy of atomisation in its series, and one of its aquated ions exists in green colour.

Find: Whether the oxide formed by that ion is neutral, acidic, basic, or amphoteric.

The solution gives the following line of reasoning:

1. The first transition series runs from Sc to Zn.
2. A green aquated ion is associated in the solution with a transition-metal ion in a lower oxidation state.
3. The hint explicitly states that for transition metals in lower oxidation states such as $+2$, the oxide formed is usually basic.
4. The worked solution then concludes that the relevant oxide is basic in nature.

Therefore, the oxide formed by the above ion is basic.

Hence, the correct option is C.

Note: The two provided approaches identify different metals, but both extracted approaches agree on the same final conclusion: the oxide is basic.