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

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.

Answer 2

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.