When you start to exercise, the body responds in various ways due to internal stimuli. one response is an increase in heart rate. identify a stimulus that would cause an increase in heart rate.
a. a decrease in body temperature
b. an increase in oxygen levels in the blood
c. a decrease in the rate of cellular respiration
d. an increase in carbon dioxide levels in the blood?

The correct answer is D) An increase in carbon dioxide level in the blood.

During exercise, contraction of muscles take place very quickly as they work harder during exercise. As more oxygen is required to burn calories efficiently, the demand for oxygen supply increases.  

When we start exercising, body temperature increases as the rate of cellular respiration also increases.

An increase in carbon dioxide in the blood causes increase in heart rate as there is more demand of oxygen for efficient contraction of the muscles.

the answer is c. it will give up it's valence electron to the other atom.