Question

When we open a gas tap of a few seconds, the sound of escaping gas is heard first but the smell of gas comes later. Why?

Answer 1

The sound of a gas travels through the vibrations of air layers, so it reaches the person faster, but the smell of a gas reaches the person through the actual movement of the air layers, so it reaches much slower. In other words, sound of gas propagates through wave and smell of gas propagates through diffusion process. Hence, the sound of gas reaches the person earlier than the smell of gas.