$A$ substance has no mass. Can one consider it as matter?

$(a)$ Enumerate the changes that take place in a liquid during evaporation.
$(b)$ How is the rate of evaporation affected by changes in the following? Justify your answer.
$(i)$ Temperature
$(ii)$ Wind speed
$(iii)$ Humidity

Which of the following will cause more severe burns and why?
$(a)$ Steam at $373 \, K$
$(b)$ Water at $373 \, K$

Why does the temperature of a substance remain constant during its melting point or boiling point?

Give a reason why gas exerts pressure on the walls of the container.

$(a)$ 'Evaporation causes cooling'. Comment on this statement.
$(b)$ Explain how water kept in an earthen pot becomes cool during summer?