Respiratory quotient (R.Q.) is defined as the ratio of a volume of `CO_2` evolved to the volume of `O_2` taken in during the respiration process. Value of R.Q. depends on the nature of respiratory substrate and to the extent to which this substance is broken down into simpler products. Which of the following situation will give us the R.Q. value as infinity when alcohol is produced?

Options

A. Fats used as substrate under aerobic conditions .
B. Organic acid is used as a substrate under aerobic conditions.
C. Carbohydrate substrate used under anaerobic conditions.
D. Any type to substrate used under aerobic conditions.

Answer

To solve the question regarding the Respiratory Quotient (R.Q.) and determine which situation will yield an R.Q. value of infinity when alcohol is produced, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of R.Q.:**
The Respiratory Quotient (R.Q.) is defined as the ratio of the volume of carbon dioxide (CO₂) evolved to the volume of oxygen (O₂) consumed during respiration. Mathematically, it is expressed as:
\[ R.Q. = \frac{\text{Volume of } CO_2 \text{ evolved}}{\text{Volume of } O_2 \text{ consumed}} \]

2. **Identify the Conditions for R.Q. to be Infinity:**
The R.Q. will approach infinity when the volume of O₂ consumed is zero while CO₂ is being produced. This can occur in anaerobic respiration where no oxygen is available.

3. **Analyze the Given Options:**
- **Option 1:** Fats used as a substrate in aerobic conditions.
- **Option 2:** Organic acid is used as a substrate under aerobic conditions.
- **Option 3:** Carbohydrate substrate is used under anaerobic conditions.
- **Option 4:** Any type of substrate used under aerobic conditions.

4. **Evaluate Each Option:**
- **Option 1:** In aerobic conditions, O₂ is consumed, so R.Q. cannot be infinity.
- **Option 2:** In aerobic conditions, O₂ is consumed, so R.Q. cannot be infinity.
- **Option 3:** In anaerobic conditions, carbohydrates are metabolized to produce alcohol and CO₂ without consuming O₂. Thus, the volume of O₂ is zero, leading to:
\[ R.Q. = \frac{\text{CO}_2 \text{ evolved}}{0} = \infty \]
- **Option 4:** In aerobic conditions, O₂ is consumed, so R.Q. cannot be infinity.

5. **Conclusion:**
The situation that will give us an R.Q. value of infinity when alcohol is produced is **Option 3: Carbohydrate substrate is used under anaerobic conditions.**