Which of the following is not an indication of a chemical reaction?
two substances burst into flames on contact.
a substance freezes.
bubbles form when two substances are combined.
a solid forms when two substances are combined.

A substance freezes

Explanation:

Two substances bursting into flames on contact can be seen as a combustion reaction, and this usually happens with very volatile substances, and is a chemical reaction that changes the substance on the atomic level.

A substance freezing simply demonstrates a phase change, and does not alter the molecule on any level, apart from the arrangement of the atoms.

Bubbles forming when two substances are combined is the indication that a gas has been formed as a product. The only way a gas can be formed is by a chemical change, usually oxygen or hydrogen is given off.

A solid forming is usually named a precipitation reaction, and the solid is called a precipitate, and this is a chemical reaction that forms an insoluble substance.

because of all the things that happen around the us, many people get into arguments which sadly could get physical, but we should actually make a change for that.

the answer is barium and copper bromide