Which of the following is not a transverse wave?

The correct answer is Option (3) → Sound waves

In a transverse wave the oscillation is perpendicular to the direction in which the wave travels. In every electromagnetic wave, the electric and magnetic fields are perpendicular to the direction of propagation. So all electromagnetic waves are transverse.

Option (1) Visible light — Transverse wave. Visible light is an electromagnetic wave, the band of the spectrum that the human eye detects.

Option (2) Heat waves — Transverse wave. Heat waves are infrared waves, the electromagnetic band just beyond the red end of the visible spectrum.

Option (3) Sound waves — Not a transverse wave. Sound in air is a longitudinal wave. The air layers vibrate back and forth along the direction of travel and form compressions and rarefactions. The wave also needs a material medium.

Option (4) Gamma rays — Transverse wave. Gamma rays are the shortest-wavelength electromagnetic waves, emitted by radioactive nuclei.

NCERT (2026-27):
Points to Ponder – “4. Most interference and diffraction effects exist even for longitudinal waves like sound in air. But polarisation phenomena are special to transverse waves like light waves.”