Which of the following wavelengths lies in the ultraviolet region?

The correct answer is Option (3) → \( 0.1\,\mu\mathrm{m} \)

The ultraviolet region covers wavelengths from about 400 nm down to 0.6 nm. With \( 1\,\mu\mathrm{m}=1000\,\mathrm{nm} \), the wavelength in nanometres is:

    \( \begin{aligned} 0.1\,\mu\mathrm{m} &= 0.1\times1000\,\mathrm{nm} \\ &= 100\,\mathrm{nm} \end{aligned} \)

Since 100 nm lies between 400 nm and 0.6 nm, this wavelength is in the ultraviolet region.

NCERT (2026-27):
Ultraviolet Rays – “It covers wavelengths ranging from about 4 × 10^–7 m (400 nm) down to 6 × 10^–10m (0.6 nm).”