Waves will have the highest speed in
air at 0°c
air at 5°c
air at 20°c
air at 30°c

The correct answer is "air at 30 degree centigrade".

Explanation:

Wave is a disturbance or energy carried out from one particle to another.

The kinetic energy is directly proportional to the temperature. The speed of the particle is more at high temperature. Then, the kinetic energy will be more at high temperature. Waves will travel with the highest speed.

Therefore, waves will have the highest speed in air at 30 degree centigrade.

thermal energy is the answer