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.

Because it sublimes (changes directly from a solid to a vapor) at room temperature. naphthalene balls are vaporisable substance so they easily turn into vapor


a) as naphthalene is a volatile substance it directly get converted into solid state to gaseous state.
b) we can get the smell of perfume sitting several meters away due to the property of diffusion. 
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.