Assertion (A): The expulsion of carbon dioxide occurs due to the increase in pressure in the thoracic cavity.
Reason (R): Exhaled air contains higher per- centage of carbon dioxide than normal air.

Options

A. Both A and Rare true and R is the cor- rect explanation for A.
B. Both A and R are true, but R is not the correct explanation for A.
C. A is true and R is false.
D. A is false and R is true.

Answer

B

Explanation

During expiration, diaphragm expands and volume of thoracic cavity decreases. Thus, the pressure in the lungs increases and exhalation takes place. Exhaled air contains higher per- centage of oxygen. Hence, the correct option is (b)