The normal stimulus to breathe is stimulated by the chemoreceptors that measure the change of what two gases?

Oxygen and carbon dioxide

Explanation:

Chemoreceptors (chemosensors) respond to a great number of blood molecules in order to maintain homeostasis (constant levels of arterial oxygen, arterial carbon dioxide, and blood pH). They can control respiratory activity, for example an increased concentration of carbon dioxide is the strongest stimulus to breathe more deeply and more frequently, and when the carbon dioxide concentration in the blood is low, the brain decreases the frequency and depth of breaths.