Which of the following is not a physical change? dissolving salt in water baking a cake melting wax freezing water

The answer can be determined through the process of elimination. If you dissolve salt in water, you can get the salt back. When you freeze water you are simply changing its state of matter. Together with the melting of wax, the three processes mentioned experience only physical change. If you bake a cake, you can't get the ingredients back therefore the second option is the correct answer.

Ais the correct answer

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).