Question

give reasons for the following observations .
(a) napthalene balls disappear with time without leaving any solid .
(b) we can get the smell of perfume  sitting several metres awa.

Answer 1

Reason-                                                                                                                                A) It is due to Sublimation-a process of matter changing from solid to gas without passing through the intermediate liquid phase. therefore Naphthalene undergoes sublimation hence converted into gaeous form. 
         B) We gt d smell of d perfume sittng several metres away bcoz of the process Diffusion.Liquid generally vaporize at normal temperature.the molecules of  perfume spread out or 'diffuse' through the air. The smell becomes less concentrated but it reaches a great distance - meaning you can smell it from far away.
tnq..

Answer 2

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(a) At room temperature, naphthalene balls undergo sublimation wherein they directly get converted from a solid to a gaseous state without having to undergo the intermediate state, i.e., the liquid state.

(b) Molecules of air move at a higher speed and have large intermolecular spaces. Perfumes comprise of flavoured substances that are volatile which scatters quickly in air, becoming less concentrated over a distance. Hence we are able to smell perfume sitting several metres away.

Hope it Helps !!