When two solutions are combined, what evidence would show a chemical reaction has occurred? *
temperature remains constant
a precipitate forms
volume increases

The presence of chemical reaction can be detected by formation of precipitate.

hence, the correct answer is

=》a precipitate forms

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.