In the air we breathe, which gas is found in the highest concentration?
Nitrogen
Water vapor
Carbon dioxide
Hydrogen
Oxygen
The Correct Answer is A
A. Nitrogen: Nitrogen makes up approximately 78% of the air we breathe, making it the most abundant gas in the atmosphere. It is largely inert and does not participate directly in human respiration.
B. Water vapor: Water vapor is present in variable amounts depending on humidity but generally constitutes a very small fraction of air, far less than nitrogen. Its concentration is not sufficient to be the highest component.
C. Carbon dioxide: Carbon dioxide is present at only about 0.04% in the atmosphere. Despite its critical role in respiration and pH regulation, it is not the major constituent of inhaled air.
D. Hydrogen: Hydrogen exists in trace amounts in the atmosphere and plays no significant role in the composition of breathable air. Its concentration is negligible compared to nitrogen or oxygen.
E. Oxygen: Oxygen makes up roughly 21% of atmospheric air, making it the second most abundant gas. While essential for cellular respiration, its concentration is much lower than that of nitrogen.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
The thymus is largest during childhood and gradually involutes after puberty, decreasing in size and activity while still producing some T lymphocytes throughout life. Similarly, the pineal gland, which regulates circadian rhythms through melatonin secretion, also undergoes gradual calcification and reduction in size with age. Both organs show age-related shrinkage.
Correct Answer is D
Explanation
A. Segmental bronchi:Each lung contains multiple segmental (tertiary) bronchi-10 in the right lung and 8–10 in the left lung. They serve individual bronchopulmonary segments, so their total exceeds five.
B. Choanae:The choanae are the paired posterior nasal apertures connecting the nasal cavity to the pharynx. There are only two, not five, and they are unrelated to the lungs.
C. Laryngeal cartilages:The larynx has several cartilages (e.g., thyroid, cricoid, arytenoid), but they number more than five and are part of the upper airway, not the lungs.
D. Lobes:The lungs are divided into five lobes total: three in the right lung (superior, middle, inferior) and two in the left lung (superior, inferior). Lobes are anatomical subdivisions important for lung function and clinical localization.
E. Tracheal cartilages:The trachea contains 16–20 C-shaped cartilaginous rings, which are far more than five. These rings support the trachea but do not describe lung anatomy.
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