Final answer:
Extremely low concentrations of oxygen in the blood are known as hypoxia, which can occur at high altitudes like the Rocky Mountains due to lower oxygen pressure.
Step-by-step explanation:
Extremely low concentrations of oxygen in the blood are known as hypoxia. This condition occurs when there is insufficient oxygen to meet the physiological needs of the tissues. Hypoxia can lead to a variety of symptoms including fatigue, headaches, and confusion. It is worth noting that the body has a very narrow range of environmental oxygen tolerance and a limited capacity to store oxygen. Conditions such as high altitudes, like those found in the Rocky Mountains, can induce hypoxia due to lower partial pressures of oxygen. Therefore, option B (Hypoxia) is the correct answer.