The first transition series metal 'M' has the highest enthalpy of atomisation in its series. One of its aquated ion (M$^{n+}$) exists in green colour. The nature of the oxide formed by the above M$^{n-}$ ion is:
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For transition metals in the lower oxidation states (such as \( +2 \)), the oxide formed is usually basic. These oxides react with acids to form salts.
The problem requires identifying the nature of the oxide formed by a transition metal 'M'. This metal exhibits the highest atomisation enthalpy within its series and forms a green aquated ion. The solution proceeds as follows:
Transition Metal Series: The first transition series encompasses elements from Scandium (Sc) to Zinc (Zn).
Atomisation Enthalpy: Atomisation enthalpy is the energy needed to convert one mole of a substance into its constituent atoms. Within the first transition series, Manganese (Mn) generally has the lowest atomisation enthalpy, while elements like Chromium (Cr) and Vanadium (V) possess relatively higher values.
Green Aquated Ions: Among the common ions in the first transition series, the chromium ion, specifically \text{Cr}^{3+} , produces a green aqueous solution.
Metal Identification: Based on both a high atomisation enthalpy and the formation of a green ion in solution, the metal 'M' is identified as Chromium (Cr).
Oxidation State and Oxide Properties: Chromium forms various oxides, including \text{CrO}_3 (acidic), \text{Cr}_2\text{O}_3 (amphoteric), and CrO (basic). Chromium(II) oxide (CrO) is the relevant oxide here and is basic.
Conclusion: The oxide of the identified metal 'M' (Chromium in a lower oxidation state) is basic in nature.
