Which of the following is not an indication of a chemical reaction?
1.) heat is generated when two substances are combined.
2.) a solid quickly forms when two liquids are combined.
3.) a substance melts when sitting in the sun.
4.) a substance sours when sitting in the sun.

Option (3) is the correct answer.

Explanation:

A reaction due to which there occurs change in chemical composition of reactants is known as a chemical reaction.

For example, evolution of heat when two substances combine together shows a chemical reaction has taken place between the substances.

Whereas a reaction which does not bring any changes in chemical composition of the reactants is known as a physical reaction.

For example, boiling point, melting point, mass, volume etc are all physical properties.

Thus, we can conclude that out of the given options a substance melts when sitting in the Sun, is not an indication of a chemical reaction.

the millers tale is the answer.

the cold front replaces the warmer air at the ground level changing the wind to be breezy and denser.there is also an immediate drop in the temperature.