Question

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:

• A. neutral
• B. acidic
• C. basic
• D. amphoteric

Hint:

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.

Answer 1

The Correct Option is C

Step 1: Identifying the Metal 'M'
The first transition series metal with the highest enthalpy of atomisation is iron (Fe). Iron has a relatively high enthalpy of atomisation compared to other metals in the first transition series.
Step 2: Analyzing the Aquated Ion
The green colour of the aquated ion \( M^{n+} \) indicates that it is likely to be a transition metal ion, as many transition metal ions exhibit characteristic colours due to d-d transitions. For iron, the \( Fe^{2+} \) ion is known to be green in colour when aquated in water. Therefore, the metal \( M \) is iron.
Step 3: Nature of the Oxide Formed
Iron forms oxides in both the \( +2 \) and \( +3 \) oxidation states. The oxide formed in the \( +2 \) oxidation state is iron(II) oxide (FeO), which is basic in nature. Basic oxides tend to react with acids to form salts and water. Therefore, the oxide formed by the \( Fe^{2+} \) ion (a metal in the \( +2 \) oxidation state) is basic.