Correct Answer: Oxygen

Solution : The correct option is - Oxygen.

Haemoglobin has the highest affinity for oxygen (O2) among the gases it can bind. This affinity allows haemoglobin to efficiently transport oxygen from the lungs to tissues throughout the body, where it is needed for cellular respiration. The binding of oxygen to haemoglobin occurs in the lungs, where the partial pressure of oxygen is high, and it releases oxygen in tissues where the partial pressure of oxygen is lower. This is a crucial process for sustaining aerobic metabolism in most living organisms.