Air has mass because it consists of particles, primarily molecules such as nitrogen, oxygen, and trace amounts of other gases. These molecules have mass and are constantly in motion, colliding with each other and with other objects. When sound waves travel through air, they do so by causing these air molecules to vibrate and propagate the disturbance.
Sound waves are mechanical waves, which means they require a medium to propagate. The vibration of air molecules transfers the energy of the sound wave from one molecule to the next, creating a chain reaction that carries the wave through the medium. Since air molecules have mass, they can be set into motion and carry the sound energy.
In contrast, light is an electromagnetic wave, and electromagnetic waves do not require a medium to propagate. They can travel through a vacuum, such as outer space, where there are no air molecules or other matter present. Light consists of oscillating electric and magnetic fields, which can travel through empty space without the need for physical particles to carry them.
The absence of a requirement for a medium is one of the fundamental properties of electromagnetic waves, including light. They can propagate through vacuum or transparent substances like air, water, or glass. While light can interact with particles and be absorbed, refracted, or scattered, the medium itself is not necessary for the light wave to exist or propagate.