Which of the following has energy unit ?

Options

A. Rate of doing work
B. Watt
C. Products of pressure and volume
D. Potential gradient.

Explanation

To determine which of the following options represents an energy unit, we need to analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Options**:
We have four options to evaluate. We need to identify which of these options is a unit of energy.

2. **Option Analysis**:
- **Option A: Rate of Doing Work**:
- The rate of doing work is defined as power. The unit of power is Watts (W), which is not a unit of energy. Therefore, this option is incorrect.

- **Option B: What**:
- This option seems to be unclear or possibly a typographical error. However, if we consider it as "Watt" again, it is a unit of power, not energy. Thus, this option is also incorrect.

- **Option C: Potential Gradient**:
- The potential gradient refers to the change in potential energy per unit distance. It is not a direct measure of energy itself, hence this option is incorrect.

- **Option D: Product of Pressure and Volume**:
- Pressure (P) is defined as force (F) per unit area (A), and volume (V) is a measure of space. The product of pressure and volume can be expressed as:
\[ P \times V = \frac{F}{A} \times V \]
When we analyze this further, we can express volume in terms of length and area:
\[ V = A \times d \quad \text{(where d is the height or length)} \]
Substituting this back, we get:
\[ P \times V = \frac{F}{A} \times (A \times d) = F \times d \]
Since work (W) is defined as force times distance (F × d), we conclude that:
\[ P \times V = W \]
Therefore, since work is equivalent to energy, the product of pressure and volume is indeed a unit of energy.

3. **Conclusion**:
The correct answer is **Option D: Product of Pressure and Volume**.