Unit used to measure nuclear diameters is 

Options

A. fermi
B. angstrom
C. micron
D. nanometre

Answer

To determine the unit used to measure nuclear diameters, we will analyze the options provided and identify which one is most suitable for measuring such small dimensions.

### Step-by-Step Solution:

1. **Understanding the Context**:
- Nuclear diameters are extremely small, typically on the order of femtometers (fm). Therefore, we need to choose a unit that can accurately represent these small measurements.

2. **Analyzing the Options**:
- **Option 1: Fermi (fm)**: This unit is commonly used in nuclear and particle physics. It is defined as \(1 \, \text{fm} = 10^{-15} \, \text{meters}\).
- **Option 2: Angstrom (Å)**: This unit is \(1 \, \text{Å} = 10^{-10} \, \text{meters}\), which is larger than a femtometer.
- **Option 3: Micron (μm)**: This unit is \(1 \, \text{μm} = 10^{-6} \, \text{meters}\), which is significantly larger than both femtometers and angstroms.
- **Option 4: Nanometer (nm)**: This unit is \(1 \, \text{nm} = 10^{-9} \, \text{meters}\), also larger than a femtometer.

3. **Identifying the Correct Unit**:
- Given that nuclear diameters are on the order of \(10^{-15}\) meters, the most appropriate unit from the options provided is the **Fermi (fm)**.

4. **Conclusion**:
- The unit used to measure nuclear diameters is the **Fermi (fm)**.

### Final Answer:
The unit used to measure nuclear diameters is **Fermi (fm)**.

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