A teacher asks students to identify which demonstrations show physical changes and which show chemical changes. Which demonstration shows a physical change?
A. Baking soda is mixed with vinegar. The mixture bubbles.
B. A dish of water is placed in the freezer. The water turns solid.
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C. A piece of pH paper is dipped in clear ammonia. The paper turns from yellow to pink.
D. Hydrogen peroxide solution is dropped on a potato slice. The liquid bubbles and fizzes.