question_answer 20)

Give reasons for the following observations :                                          (a) Naphthalene balls disappear with time without leaving any solid.                  (b) We can get the smell of perfume sitting several metres away.  

Answer:

(a): Naphthalene balls disappear with time without leaving any solid because they undergo sublimation i.e., they directly change into vapour without passing through the liquid state.   (b): We can get the smell of perfume sitting several metres away due to diffusion. The perfumes contain solvent which carries pleasant smelling vapour. They diffuse quite fast and can reach a person sitting several metres away.