Question: which one of the following is not an electromagnetic radiation?
Answer: Since electromagnetic waves always travel at the speed of light in their current medium we can immediately say that sound waves are not electromagnetic waves, since they travel at the speed of sound (≈334 m/s) which is much much less than the speed of light in air (≈299,700,000 ≈ 299 , 700 , 000 m/s).