Crocodile hemoglobin does not bind 2,3-BPG. Instead, it binds bicarbonate ion, which is a strong negative allosteric effector. Why might crocodiles have a hemoglobin that is responsive to HCO−3 instead of 2,3-BPG? Recall that crocodiles hold their prey underwater to kill them. a. As the crocodile stays underwater, its hemoglobin delivers most of the bound HCO−3 as a result of decreased binding of O2 to the R conformation.
b. As the crocodile stays underwater, its hemoglobin delivers most of the bound O2 as a result of increased binding of HCO−3 to the T conformation.
c. As the crocodile stays underwater, its hemoglobin delivers most of the bound O2 as a result of decreased binding of HCO−3 to the R conformation.
d. As the crocodile stays underwater, its hemoglobin delivers most of the bound HCO−3 as a result of increased binding of O2 to the T conformation.

Explanation:

In tissues CO2 enter in red blood cells and converted into HCO-3 with the release of H+ ion;reaction is catalysed by carbonic anhydrase enzyme

Released H+ ions reduces pH of cells and facilitate dissociation of oxygen from hemoglobin

This is favored by T state which occurs in tissues

Hemoglobin mainly exists in two conformations: T state and R state

T state consists of deoxygenated hemoglobin,less affinity for oxygen and is favored by tissues

R state consists of oxygenated hemoglobin,high affinity for oxygen and is favored by lungs

T state is dominant conformation of deoxy hemoglobin and stabilized by ionic interactions whereas oxygen binding stabilizes R state

Here in case of crocodile,underwater there is increased binding of HC0-3 to the T state because there is less affinity for oxygen underwater hence T state will be dominant

and after water is usually warmed by the sun the water temperature raises and then evaporates .