Some of the physical changes of matter can be arranged in
pairs to show that they are
reversible reactions.

a) Identify a pair of physical
changes between a solid
and liquid.

b) Identify two pairs of physical
changes between a liquid
and a gas.

when liquid is cooled it gets converted into its solid form. so,in this the condition is being reversed.so it is reversible change. Similarly,liquid when heated it gets converted into its gaseous form. when,gas is cooled,it gets converted into its liquid form

I think answer is B

heat or electricity in the atmosphere- c.