Which of the following statements is NOT true about X-rays?

The correct answer is Option (2) → Frequency range: \( 10^{11}\,\mathrm{Hz} - 10^{14}\,\mathrm{Hz} \)

X-rays lie in the electromagnetic spectrum beyond ultraviolet, with wavelengths from about \( 100\,\mathring{\mathrm{A}} \) down to \( 10^{-3}\,\mathring{\mathrm{A}} \) and frequencies of about \( 10^{16} \) to \( 10^{21}\,\mathrm{Hz} \) (from \( \nu = c/\lambda \)). They are produced when fast electrons are stopped by a metal target.

Option (1) Wavelength Range: \( 100\,\mathring{\mathrm{A}} - 0.1\,\mathring{\mathrm{A}} \) (angstrom) — True. \( 100\,\mathring{\mathrm{A}} \) to \( 0.1\,\mathring{\mathrm{A}} \) lies within the X-ray range.

Option (2) Frequency range: \( 10^{11}\,\mathrm{Hz} - 10^{14}\,\mathrm{Hz} \) — NOT true. \( 10^{11} \) to \( 10^{14}\,\mathrm{Hz} \) is the microwave and infrared region; the X-ray frequencies are many orders of magnitude higher. This is the answer.

Option (3) Source: sudden deceleration of fast moving electrons by a metal target — True. Sudden deceleration of fast electrons on a metal target gives X-rays.

Option (4) More energetic than UV rays — True. X-rays have a higher frequency than ultraviolet rays, so each photon carries more energy.

NCERT (2026-27):
X-Rays – “Beyond the UV region of the electromagnetic spectrum lies the X-ray region. We are familiar with X-rays because of its medical applications. It covers wavelengths from about 10⁻⁸ m (10 nm) down to 10⁻¹³ m (10⁻⁴ nm). One common way to generate X-rays is to bombard a metal target by high energy electrons.”