Question

1. Which of these observations is an indication that a chemical reaction has occurred?

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1 point
Steam forms above boiling water.
A solid forms when a clear solution is frozen.
A solid forms when two clear solutions are mixed.
Sugar crystals form on the sides of a boiling pot of sugar water.

Answer 1

"A solid forms when two clear solutions are mixed."

This indicates a chemical reaction because a precipitate (a new substance) is produced when the solutions react. The other options are physical changes (phase changes or crystallization of the original substance).