X-rays of wavelength, λ=1 mathrmmathringA have frequency:

The correct answer is Option (4) → \( 3\times10^{18} \) Hz

All electromagnetic waves travel in vacuum with the speed of light, so \( c = \nu\lambda \). The wavelength is \( 1\,\mathrm{\mathring{A}} = 10^{-10}\,\mathrm{m} \).

    \( \displaystyle \nu = \frac{c}{\lambda} = \frac{3\times10^{8}\,\mathrm{m\,s^{-1}}}{1\times10^{-10}\,\mathrm{m}} = 3\times10^{18}\,\mathrm{Hz} \)

Shortcut: For a wavelength given in angstrom, \( \nu = \frac{3\times10^{18}}{\lambda(\mathrm{\mathring{A}})}\,\mathrm{Hz} \). For \( 1\,\mathrm{\mathring{A}} \) this is \( 3\times10^{18}\,\mathrm{Hz} \) directly.

Note: A similar question was also asked in CUET (UG) 2023 on 23-05-2023 (Slot 3).