Which of the following substances can increase the affinity of hemoglobin for oxygen, thereby reducing oxygen delivery to tissues?

A Carbon monoxide ✓
B Cyanide
C Nitric oxide
D Hydrogen sulfide

Explanation

Carbon monoxide (CO) binds to hemoglobin with high affinity, forming carboxyhemoglobin, which increases the affinity of hemoglobin for oxygen and reduces oxygen delivery to tissues.

Source

Harrison's Principles of Internal Medicine
Hematology Hematology: Hemoglobin and Oxygen Transport Hematology: Hemoglobin and Oxygen Transport Hard MEDICAL Confidence: high