[k42490]

I have a question about Henry's law, which I know says that the amount of gas dissolved is proportional to the gas pressure above solution.

My question says: the weak electrolyte NH₃ does not obey Henry's law, and O₂ obeys Henry's law in water but not in blood (aqueous solution ). Why?

for NH₃, I think it is because it is a weak electrolye and will dissociate in solution,  but I do not know about the O₂

[Yggdrasil]

You are correct about the ammonia.  For the blood question, think about if there is anything in blood that might affect the dissolved O₂ (e.g. by binding it).

[IITian]

Inside the lungs, the diffusion of oxygen into the blood triggers the reactions. The oxygen reacts with and attaches to hemoglobin (an iron containing pigment). This oxygenation reaction with hemoglobin produces excess H+ ions which react with HCO₃^3- to produce H₂CO₃. The carbonic acid decomposes to CO₂ which diffuses out of the blood.