Which of the following is most clearly an example of a physical change? a. a solid dissolves when added to a liquid b. a solution changes color when something is added c. two liquids produce heat when mixed together d. a gas is released when two solutions are combined

Physical change is described as the change that affects the form of a chemical compound but not its chemical composition. It involves the change in physical properties.

When a solid is dissolved in the liquid the solid gets dissolved in the liquid there is no breakage in the bonds and same composition of the compounds are at the end of the change. When a solution changes colour due to the addition of an other substance the bonds are broken or formed between molecules or atoms. The substance with a certain set of properties is turned into different substance with different properties. Hence it is a chemical change.

Two liquids producing heat when mixed together results in the temperature change. The heat is produced due to the increase in the temperature. Hence it is a chemical change.

When two solutions are combined gas is released due to the temperature change. This is also a chemical change

Therefore the answer is A.

particle   p is an electron and particle q is a neutron