Which of the following units are used frequently for atomic radii?

Options

A. Meter
B. Picometres
C. Kilometers
D. Centimeters

Explanation

To determine which units are frequently used for atomic radii, we can analyze the options provided: meter, picometer, kilometer, and centimeter.

### Step-by-Step Solution:

1. **Understanding Atomic Radii**: Atomic radii refer to the size of an atom, typically measured as the distance from the nucleus to the outer boundary of the surrounding cloud of electrons. This distance is very small, as atoms are on the order of picometers.

2. **Evaluating the Units**:
- **Meter (m)**: This is a standard unit of length but is too large for atomic measurements. Atomic radii are generally much smaller than a meter.
- **Picometer (pm)**: This unit is equal to \(10^{-12}\) meters. It is specifically used for measuring atomic and molecular dimensions, making it suitable for atomic radii.
- **Kilometer (km)**: This unit is used for measuring larger distances (1 km = \(10^3\) m) and is not applicable for atomic scales.
- **Centimeter (cm)**: This unit is equal to \(10^{-2}\) meters. While smaller than a meter, it is still too large for atomic measurements.

3. **Conclusion**: Among the given options, the picometer is the most appropriate unit for measuring atomic radii due to its scale. Therefore, the correct answer is **picometer**.

### Final Answer:
The unit frequently used for atomic radii is **picometer**.

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