Question

give reason for the following observations .
a)naphthalene balls dissappear with time living any solid.
b)our palm feel cold when we pat some acetone or petrol or perfume on it.​

Answer 1

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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. ... The perfumes contain solvent which carries pleasant smelling vapour.

b) . When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of the liquid absorb energy from the surface of the palm to compensate for the loss of energy, making the surroundings cool. Hence, our palm feels cold when we put some acetone or petrol or perfume on it.

Answer 2

a. ans in above pic. (sry 4 bad handwriting)

b. Acetone,petrol and perfume are volatile substance that gets evaporated when they come in contact with air Evaporation is facilitated as it uses energy from the palm hence leaving a cooling effect on our palms.