Option 1 -> Sound travels through air as a longitudinal wave, which is how we hear most everyday sounds.
Option 2 -> Sound travels through water and actually moves faster in water than in air due to water's greater density.
Option 3 -> Sound travels through steel very efficiently; solids are excellent conductors of sound waves.
Option 4 -> Sound cannot travel through a vacuum because it requires a medium (particles) to propagate, and a vacuum contains no matter.
Hence, Option 4: Vacuum -> Sound is a mechanical wave that needs particles to vibrate and transfer energy. Since a vacuum is empty space with no particles, sound waves cannot propagate through it. This is why there is no sound in outer space. -> correct