X-rays are electromagnetic radiation whose wavelengths are of the order of:

The correct answer is Option 4 (10-10 metre).

X-rays are high-energy electromagnetic waves discovered by Wilhelm Röntgen. In the electromagnetic spectrum, X-rays occupy the region between ultraviolet light and gamma rays. Their characteristic wavelengths typically range from 0.01 to 10 nanometres (10-11 to 10-8 metres).

The significance of 10-10 metre (also known as 1 Angstrom) is twofold:

• It represents the typical interatomic spacing in crystalline solids, which allows X-rays to be used in crystallography/diffraction studies.
• It corresponds to the scale of the electron cloud of an atom.

Other options are incorrect because:

• 1 metre falls in the Radio wave spectrum.
• 10-1 metre (10 cm) belongs to Microwaves.
• 10-5 metre (10 microns) is in the Infrared region.

Therefore, 10-10 metre is the most accurate order of magnitude for X-ray wavelengths.