A) A gas was produced.
In a chemical change there is always a change in the chemical composition. When reactant reacts with one another new products are formed, the products have a different chemical composition than the reactants. Option A is correct as gases have evolved as a result of chemical change.
Option B and D are physical changes therefore incorrect. When matter dissolves in water or mixes with another substance there is no change in the chemical composition of the said matter.
Option C is incorrect as change in temperature is a change in the kinetic energy of matter and is not a chemical change.