An antitranspirant is

Options

A. Phenyl mercuric acid
B. Abscisic acid
C. Salicylic acid
D. All the above

Answer

To answer the question "An antitranspirant is," we will analyze the options provided and understand what antitranspirants are.

### Step-by-Step Solution:

1. **Understanding Antitranspirants**:
- Antitranspirants are substances that are applied to the leaves of plants to reduce the rate of transpiration. Transpiration is the process through which water vapor is lost from the plant to the atmosphere, primarily through small openings called stomata.

2. **Analyzing the Options**:
- **Option A: Phenylmercuric Acid**: This is known to be an antitranspirant as it helps in reducing transpiration by closing the stomata.
- **Option B: Abscisic Acid**: This is a plant hormone that plays a crucial role in regulating transpiration by causing the stomata to close, thus reducing water loss.
- **Option C: Salicylic Acid (Aspirin)**: Salicylic acid is also known to have antitranspirant properties, as it can influence stomatal closure and reduce transpiration.
- **Option D: All of the Above**: Since all the mentioned compounds (phenylmercuric acid, abscisic acid, and salicylic acid) have antitranspirant properties, this option suggests that all of them are antitranspirants.

3. **Conclusion**:
- Since all three compounds listed in the options are recognized as antitranspirants, the correct answer is **Option D: All of the Above**.

### Final Answer:
**D. All of the above**