Final answer:
The actual (absolute) intra-alveolar pressure at rest, which is described as zero relative to atmospheric pressure, is actually 760 mmHg, the same as atmospheric pressure.
Step-by-step explanation:
The question is about the pressure inside the alveoli, known as intra-alveolar pressure, at rest relative to atmospheric pressure. Atmospheric pressure is approximately 760 mmHg, which is also the pressure at sea level. When the intra-alveolar pressure is said to be zero at rest, it means that it is equal to the atmospheric pressure, not that it actually has a value of 0 mmHg. Therefore, the actual (absolute) intra-alveolar pressure at rest is 760 mmHg, which means it equalizes with the atmospheric pressure.
It's important to note that negative pressure is lower than atmospheric pressure, and positive pressure is higher. At rest, the intra-alveolar pressure is indeed zero relative to atmospheric pressure; however, this is an expression of equilibrium rather than a literal value of zero. Hence, option a) 760 mmHg (equal to atmospheric pressure) is the correct answer.