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.

Define the following terms: $(i)$ Rigidity,$(ii)$ Compressibility,and $(iii)$ Density. Compare any two states of matter on the basis of the above-defined properties.

Fill in the blanks :
$(a)$ Evaporation of a liquid at room temperature leads to a ........... effect.
$(b)$ At room temperature,the forces of attraction between the particles of solid substances are ........... than those which exist in the gaseous state.
$(c)$ The arrangement of particles is less ordered in the ........... state. However,there is no order in the ........... state.
$(d)$ ........... is the change of solid state directly to vapour state without going through the ........... state.
$(e)$ The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called ...........

$(a)$ Define boiling point.
$(b)$ Express the boiling point of water in Celsius as well as Kelvin scale.
$(c)$ $A$ diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

$2 \, mL$ of Dettol is added to a beaker containing $500 \, mL$ of water and stirred. State four observations that you make.

$A$ student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following graphs would correctly represent the result? Justify your choice.