Question

why does smell of hot cooked food reaches several metres away within seconds

Answer 1

Due to kinetic energy. Since, the smell coming out is in the form of hot rays from the hot food, and so it has high temperature which makes it lighter than the air and also it would have high kinetic energy increases the rate of diffusion and the smell reaches to a long distance in less time. 

Answer 2

This process is called diffusion. Movement of particles from higher concentration to lower concentration is called diffusion. Diffusion occurs in liquids and gases but not in solids. As molecules of gases are loosely packed than in liquids diffusion is faster in gases compared to liquids. That is the reason we are able to smell particles from long distances