Answer:
the formation of a gas
Explanation:
The chemical change is one in which some chemical reaction occur.
a) Phase change : it is simply change of one state of matter to another.
For example conversion of ice to liquid water, where there is no change in chemical composition of water and only the physical state is changing.
b) formation of gas: it is possible when some substance breaks into some other components or some substance reacts with other. This is definitely a chemical change as bonds will break and may be new bonds will form.
For example decomposition of calcium carbonate gives carbon dioxide (a gas) and calcium oxide.
c) mass change: it could be due to evaporation of water from a substance. Which must be a physical change.
d) surface area: change in surface is area must be due to change in state or physical modifications in state of a substance.
