In which of the following steps of citric acid cycle, `CO_(2)` is evolved
I. Citric acid `rarr alpha`-ketoglutaric acid.
II. Succinic acid `rarr` malic acid III. Malic acid `rarr` oxaloacetic acid IV. `alpha`-Ketoglutaric acid `rarr` succinyl CoA

Options

A. I and II
B. I and IV
C. II and III
D. II and IV

Answer

To determine in which steps of the citric acid cycle carbon dioxide (CO₂) is evolved, we need to analyze each of the given steps:

1. **Citric acid → α-ketoglutaric acid**:
- This step involves the conversion of citric acid (a 6-carbon compound) to α-ketoglutaric acid (a 5-carbon compound) through a decarboxylation reaction. During this process, one molecule of CO₂ is released.

2. **Succinic acid → Malic acid**:
- In this step, succinic acid (a 4-carbon compound) is converted to malic acid (another 4-carbon compound). Since both compounds have the same number of carbon atoms, no CO₂ is released in this reaction.

3. **Malic acid → Oxaloacetic acid**:
- This step involves the conversion of malic acid (a 4-carbon compound) to oxaloacetic acid (another 4-carbon compound). Similar to the previous step, there is no change in the number of carbon atoms, so no CO₂ is released here either.

4. **α-Ketoglutaric acid → Succinyl CoA**:
- This step involves the conversion of α-ketoglutaric acid (a 5-carbon compound) to succinyl CoA (a 4-carbon compound) through another decarboxylation reaction. During this reaction, one molecule of CO₂ is released.

### Summary of CO₂ Evolution:
- CO₂ is evolved in:
- Step I: Citric acid → α-ketoglutaric acid
- Step IV: α-Ketoglutaric acid → Succinyl CoA

### Final Answer:
The correct steps where CO₂ is evolved are:
- I. Citric acid → α-ketoglutaric acid
- IV. α-Ketoglutaric acid → Succinyl CoA