Ben and jerry were testing powders in science lab. first they put the powder in a zip lock bag. next they added some water. the powder fizzed and bubbled; soon it disappeared. when the bubbling stopped the bag contained a clear liquid and a lot of gas. what is the most obvious sign of a chemical change in this reaction. a) a gas was produced. b) the powder mixed with the water. c) there was a change in temperature. d) the powder dissolved in the water.

A)A gas was produced.

Explanation:

In a chemical change there is always a change in the chemical composition. When reactant reacts with one another new products are formed, the products have a different chemical composition than the reactants.  Option A is correct as gases have evolved as a result of chemical change.

Option B and D are physical changes therefore incorrect. When matter dissolves in water or mixes with another substance there is no change in the chemical composition of the said matter.

Option C is incorrect as change in temperature is a change in the kinetic energy of matter and is not a chemical change.