Which of the following is an electromagnetic wave?

The correct answer is Option (4) → Infrared waves

An electromagnetic wave is made of oscillating electric and magnetic fields that travel through space, even through vacuum, at the speed of light.

Option (1) Alpha rays — Incorrect. Alpha rays are a stream of alpha particles, which are the nuclei of helium atoms. Each carries a charge of 2e. They are material particles. They are not oscillating fields.

Option (2) Sound waves — Incorrect. Sound is a mechanical, longitudinal wave of the medium itself and cannot travel through vacuum.

Option (3) Matter waves — Incorrect. Matter waves, or de Broglie waves, are the waves associated with moving material particles such as electrons.

Option (4) Infrared waves — Correct. Infrared waves form a band of the electromagnetic spectrum next to the long-wavelength (red) end of visible light. Hot bodies and molecules give out these waves.

NCERT (2026-27):
Electromagnetic Spectrum – “… By the end of the nineteenth century, X-rays and gamma rays had also been discovered. We now know that, electromagnetic waves include visible light waves, X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves.”