Waves which can only travel through a medium are called mechanical waves. Which one of the following is not a mechanical wave?

Waves which can only travel through a medium are called mechanical waves. Which one of the following is not a mechanical wave?

لہریں جو صرف ایک میڈیم کے ذریعے سفر کرسکتی ہیں انہیں مکینیکل لہریں کہتے ہیں۔ مندرجہ ذیل میں سے کون سا مکینیکل لہر نہیں ہے؟
Explanation

Infra-red waves are electromagnetic waves and do not require a medium to travel.

Mechanical waves like water, sound, and seismic waves need a medium (solid, liquid, or gas) to propagate.