Assertion : When carbohydrates are used as substrate and are completely oxidised, the RQ is equal to 1.
Reason : When proteins are used in respiration, the RQ is greater than 1.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To analyze the question effectively, we need to break it down into its components: the assertion and the reason.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that when carbohydrates are used as a substrate and are completely oxidized, the respiratory quotient (RQ) is equal to 1.
- RQ is defined as the ratio of carbon dioxide produced to oxygen consumed during respiration.
- For carbohydrates, which are primarily composed of carbon, hydrogen, and oxygen, the complete oxidation typically results in equal amounts of CO2 produced and O2 consumed, leading to an RQ of 1.

2. **Understanding the Reason**:
- The reason states that when proteins are used in respiration, the RQ is greater than 1.
- However, this is incorrect. When proteins are used as substrates, the RQ is actually less than 1, usually around 0.9. This is because the oxidation of proteins involves the deamination of amino acids, which results in the production of less CO2 relative to the amount of O2 consumed.

3. **Conclusion**:
- Based on the above analysis, the assertion is true because carbohydrates do yield an RQ of 1 when completely oxidized.
- The reason is false because the RQ for proteins is less than 1, not greater than 1.

4. **Final Answer**:
- The correct conclusion is that the assertion is true, but the reason is false.

### Summary:
- **Assertion**: True (RQ for carbohydrates = 1)
- **Reason**: False (RQ for proteins < 1)