Metals And Non Metals

The question focuses on identifying the nature of the oxide formed by a transition metal 'M' that has the highest enthalpy of atomisation in its series, and where its aquated ion exists in green color. Let's break down the solution step-by-step:

1. Understanding the Transition Metal Series: The first transition series ranges from Scandium (Sc) to Zinc (Zn).
2. Enthalpy of Atomisation: Enthalpy of atomisation refers to the energy required to break one mole of a substance into its constituent atoms. In the first transition series, Manganese (Mn) typically has the lowest, and elements like Chromium (Cr) and Vanadium (V) have relatively higher enthalpies of atomisation.
3. Green-Colored Aquated Ions: Among the common ions in the first transition series, the chromium ion, specifically \text{Cr}^{3+} , forms a green-colored aqueous solution.
4. Identifying the Metal: Considering both the high atomisation enthalpy and the green color of the ion, Chromium (Cr) is identified as 'M'.
5. Oxidation State and Oxide Nature: Chromium can form different oxides like \text{CrO}_3 (acidic), \text{Cr}_2\text{O}_3 (amphoteric), and CrO (basic). The oxide relevant here is Chromium(II) oxide (CrO), which is basic.
6. Conclusion: The oxide formed by the metal 'M' identified as Chromium (in the lower oxidation state) is basic in nature.

Therefore, the correct answer is basic.