Which of the following is an example of a physical change? O A. A gas is given off when two substances are mixed.
B. A copper rod is hammered into a thin sheet.
C. A solid forms when two clear liquids are mixed.
O D. A matchstick changes color when it burns.

A gas is given off when two substances are mixed.

physical change: A copper rod is hammered into a thin sheet.

A solid forms when two clear liquids are mixed.

A matchstick changes color when it burns.

explanation

a physicals change vs chemical

physical change is like cutting, changing shape etc, it the molecules that make it and the chemicals of it stay same

chemical change when it chemically changed such as cooking meat

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.