For which of the following elements it is difficult to disproportionate
in +3 oxidation state?

Options

A. N
B. As
C. Sb
D. Bi

Answer

To solve the question regarding which element has difficulty in disproportionating in the +3 oxidation state, we will analyze the elements in Group 15 and their oxidation states.

### Step-by-Step Solution:

1. **Understanding Disproportionation**:
Disproportionation is a reaction where an element in one oxidation state is simultaneously oxidized and reduced to form two different products.

2. **Identifying Group 15 Elements**:
The elements in Group 15 are Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi).

3. **Oxidation States of Group 15 Elements**:
- Nitrogen can exhibit oxidation states from -3 to +5.
- Phosphorus can show oxidation states from -3 to +5.
- Arsenic can show oxidation states from -3 to +5.
- Antimony can show oxidation states from -3 to +5.
- Bismuth can show oxidation states from +3 to +5.

4. **Disproportionation in Acidic Medium**:
- Nitrogen and phosphorus readily undergo disproportionation in acidic medium due to their ability to exist in multiple oxidation states.
- For example, nitrogen in HNO3 can disproportionate to form NO and H2O.

5. **Trend in Stability of +3 Oxidation State**:
As we move down the group from nitrogen to bismuth, the stability of the +3 oxidation state increases due to the inert pair effect. This means that the +3 oxidation state becomes more stable and less likely to undergo disproportionation.

6. **Conclusion**:
Since bismuth is the heaviest element in the group and exhibits a stable +3 oxidation state, it is the element for which it is difficult to disproportionate in the +3 oxidation state.

Therefore, the answer to the question is **Bismuth (Bi)**.