Question

which indicator of a chemical reaction is shown in the picture? the formation of a gas the formation of a precipitate a change in energy

Explanation:

In the picture, bubbles are visible in the test - tube, which is a sign of gas formation during a chemical reaction. Formation of a precipitate would be a solid settling out, and a change in energy might be indicated by heat or light, but neither of those are obvious here.

Answer:

the formation of a gas