Verifying gas percentage statements in inspired/expired air

Steps:

• Calculate inspired air O2/CO2 ratio: 21% / 0.04% = 525 times.
• Compare expired CO2: exercising 6.54% vs. resting 5.04%, difference 1.5%.
• Check resting O2: inspired 21%, expired 16%, difference 5%.
• Assess O2 usage: resting drop 5% (21-16), exercising 5.6% (21-15.4), similar percentages.

Why C is correct:

• Inspired O2 is 525 times CO2 (21 / 0.04 = 525), not 5.25 times, due to miscalculation of ratio.

Why the others are wrong:

• A: Difference in expired CO2 (6.54% - 5.04% = 1.5%) is correct based on data.
• B: Resting expired O2 is 16% (inspired 21%), a valid 5% reduction from table.
• D: O2 usage similar (~5-5.6% drop from 21%) in both conditions, consistent with respiration demands.

Final answer: C