In atomic physics, atomic radius is most conveniently measured in which of the following units?

Introduction / Context:
This question belongs to basic physics and chemistry. It asks which unit is appropriate for measuring atomic radius, a very small distance describing the size of an atom. Choosing the right unit shows that you understand the scale of atomic structures compared with everyday measurements.

Given Data / Assumptions:

• The quantity in question is atomic radius, typically of the order of 10^(-10) metres.
• Options include micrometres, nanometres, millimetres, and centimetres.
• Knowledge of metric prefixes and their magnitude is assumed.

Concept / Approach:
Metric prefixes help express very large or very small quantities. One centimetre is 10^(-2) metres, one millimetre is 10^(-3) metres, one micrometre is 10^(-6) metres, and one nanometre is 10^(-9) metres. Atomic radii are usually of the order of 0.1 nanometre, or 1 angstrom, which is 10^(-10) metres. While angstrom is commonly used in specialised contexts, in the metric system nanometre is a convenient unit. Micrometres, millimetres, and centimetres are much larger and are used for cells, grains of sand, and everyday objects, not for atoms.

Step-by-Step Solution:

Verification / Alternative check:
Chemistry textbooks often provide tables of atomic radii in units such as picometres or angstroms. One angstrom is 0.1 nanometre. When values are expressed in the metric system alone, authors sometimes choose nanometres or picometres to avoid very small decimal numbers. This practice confirms that nanometres are suitable and commonly used for atomic scales, while micrometres and larger units are not practical for such tiny distances.

Why Other Options Are Wrong:

Micrometres, which are too large for atomic dimensions, is incorrect because a micrometre is the scale of cells and bacteria, far larger than an atom.

Millimetres, typically used for everyday objects, is incorrect because a millimetre is about the thickness of a credit card and is many orders of magnitude larger than atomic dimensions.

Centimetres, much larger than atomic scales, is clearly wrong because centimetres are used for measuring simple lengths like pen caps or small distances on a ruler.

Common Pitfalls:
Students sometimes misremember the order of metric prefixes and think that micrometres or even millimetres are small enough for atoms. Another pitfall is ignoring powers of ten and choosing a unit that simply sounds technical. To avoid this, always translate the prefixes into powers of ten and compare them with typical sizes of the objects, such as atoms, cells, or people. Recognising that atoms are around 10^(-10) metres immediately tells you that nanometres or smaller units are appropriate.

Final Answer:
Atomic radius is most conveniently measured in Nanometres, suitable for expressing very small atomic sizes.