Annie performed an experiment in her kitchen. She poured 2 cups of water in a large glass. She added three drops of green food coloring to the water. The water slowly turned green. She added an Alka-Seltzer® tablet to the water. The tablet began to fizz and create bubbles in the water. Which of the following is evidence of a chemical change in Annie's experiment?
flammability
color change
change of state
formation of a gas