How does carbon monoxide affect the oxygen-carrying capacity of hemoglobin?

A Carbon monoxide increases the oxygen-carrying capacity of hemoglobin by binding to the heme group
B Carbon monoxide decreases the oxygen-carrying capacity of hemoglobin by competing with oxygen for binding sites ✓
C Carbon monoxide has no effect on the oxygen-carrying capacity of hemoglobin
D Carbon monoxide increases the affinity of hemoglobin for oxygen, allowing it to bind oxygen more tightly

Explanation

Carbon monoxide binds to the heme group of hemoglobin with high affinity, competing with oxygen for binding sites and reducing the oxygen-carrying capacity of hemoglobin.

Source

Robbins and Cotran Pathologic Basis of Disease
Hematology Hematology: Hemoglobin and Oxygen Transport Hematology: Hemoglobin and Oxygen Transport Hard MEDICAL Confidence: high