Question

Assertion (A): Cigarette smoking decreases the oxygen levels in blood. Reason (R): Carbon monoxide interferes with the transport of oxygen by the haemoglobin.

• A. Both (A) and (R) are true, (R) is the correct explanation for (A)
• B. Both (A) and (R) are true, (R) is not the correct explanation for (A)
• C. (A) is true, but (R) is false
• D. (A) is false, but (R) is true

Hint:

Carbon monoxide has about 200 times greater affinity for haemoglobin than oxygen.

Answer 1

The Correct Option is A

Concept: Carbon monoxide present in cigarette smoke binds strongly with haemoglobin and reduces oxygen transport.

Step 1: Analyse the Assertion.
Smoking introduces carbon monoxide into blood. This decreases oxygen carrying capacity. Hence, \[ \boxed{\text{Assertion is True}} \]

Step 2: Analyse the Reason.
Carbon monoxide combines with haemoglobin. \[ Hb + CO \rightarrow HbCO \] where HbCO denotes carboxyhaemoglobin. Hence, \[ \boxed{\text{Reason is True}} \]

Step 3: Check the explanation.
Because haemoglobin becomes occupied by CO, oxygen transport decreases. Thus the reason directly explains the assertion. \[ \boxed{\text{Option (A)}} \]