Design an experiment that determines the amount of time needed for a person’s heart rate to return to normal after exercise

You could record yourself doing a cardio exercise such as running or using a jump rope for a certain period of time using a stop watch or a phone timer. Then stop after about 5-10 minutes and using the stop watch see how long it takes for your heart rate to go back to normal.

Explanation:

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

maritime tropical may be your answer.