R.Q. of 4 is obtained when respiratory substrate is

Options

A. Oxalic acid
B. Malic acid
C. Tartaric acid
D. Glucose.

Answer

To solve the question regarding which respiratory substrate yields an R.Q. (Respiratory Quotient) of 4, we can follow these steps:

### Step-by-Step Solution:

1. **Understand R.Q.**: R.Q. is defined as the ratio of the volume of carbon dioxide (CO2) produced to the volume of oxygen (O2) consumed during respiration. It is calculated using the formula:
\[ R.Q. = \frac{\text{Volume of CO2 evolved}}{\text{Volume of O2 consumed}} \]

2. **Identify R.Q. Values for Different Substrates**:
- Carbohydrates (e.g., glucose) typically have an R.Q. of 1.
- Proteins have an R.Q. of approximately 0.9.
- Fats have an R.Q. of around 0.7.
- Organic acids generally have an R.Q. greater than 1.

3. **Examine the Options**:
- **Option A: Oxalic Acid** - Known to have an R.Q. of about 4.
- **Option B: Malic Acid** - Has an R.Q. of approximately 1.33.
- **Option C: Tartaric Acid** - Has an R.Q. of about 1.6.
- **Option D: Glucose** - As a carbohydrate, it has an R.Q. of 1.

4. **Determine the Correct Answer**: Since we are looking for a substrate with an R.Q. of 4, we find that:
- **Oxalic Acid** is the only option that matches this criterion.

5. **Conclusion**: Therefore, the respiratory substrate that yields an R.Q. of 4 is **Oxalic Acid**.

### Final Answer:
The respiratory substrate that yields an R.Q. of 4 is **Oxalic Acid**.

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