Sound waves are not electromagnetic waves because

The correct answer is Option (4) → they cannot pass through vacuum

An electromagnetic wave is made of electric and magnetic fields that vibrate and keep each other going. No material medium takes part, so these waves travel through vacuum. Sound is a mechanical wave. It needs the particles of a medium such as air to travel.

Option (1) they undergo interference — Incorrect. Interference is shown by all waves, sound and light alike. So it cannot separate sound from electromagnetic waves.

Option (2) they undergo diffraction — Incorrect. Sound bends round corners and light shows diffraction too. Diffraction is common to both kinds of wave.

Option (3) they undergo reflection — Incorrect. Sound is reflected from a wall and we hear an echo. Light is reflected by a mirror. Both kinds of wave are reflected, so reflection cannot tell them apart.

Option (4) they cannot pass through vacuum — Correct. Sound needs a medium and cannot travel through vacuum, while electromagnetic waves can. This is why sound is not an electromagnetic wave.

NCERT (2026-27):
Nature of electromagnetic waves – “They are self-sustaining oscillations of electric and magnetic fields in free space, or vacuum. They differ from all the other waves we have studied so far, in respect that no material medium is involved in the vibrations of the electric and magnetic fields.”