Which of the following is a unit that of force?

Options

A. `Nm`
B. `mN`
C. `Nm^2`
D. `Ns`

Answer

To determine which of the given options is a unit of force, we will analyze each option based on our knowledge of the units of force.

### Step-by-Step Solution:

1. **Understand the SI Unit of Force**:
- The SI unit of force is the Newton (N).

2. **Evaluate Each Option**:
- **Option 1: Newton meter (N·m)**
- This unit represents torque or work done (force multiplied by distance). Therefore, it is not a unit of force.

- **Option 2: Milli Newton (mN)**
- A milli Newton is equal to \(1 \times 10^{-3}\) Newtons. Since it is a smaller unit of Newton, it is indeed a unit of force. This option is correct.

- **Option 3: Newton meter square (N·m²)**
- This unit represents the moment of inertia or other quantities involving force and area. It is not a unit of force.

- **Option 4: Newton second (N·s)**
- This unit represents impulse (force multiplied by time). Therefore, it is not a unit of force.

3. **Conclusion**:
- The only option that is a unit of force is **Option 2: Milli Newton (mN)**.

### Final Answer:
The unit of force among the given options is **Milli Newton (mN)**.