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Question 3

Give reason 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) Some substances possess the property of sublimation like camphor and naphthalene balls. Such substances directly change from solid to gaseous state without changing in to liquid like:



               ice → water  water vapour does.

Therefore, naphthalene balls disappear with time without leaving any solid. 
(Sublimation - Solid to gaseous state directly converted).

 

(b) Being a volatile substance (gets evaporated easily) perfume changes from liquid to gaseous state very fast. Those particles mix up with air particles and diffuse to reach our nostrils such that we get the smell of perfume sitting several metres away.

(volatile substance  liquid to gaseous state changed immediately).

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