Discussion
Carbon monoxide poisoning happens due to :
Answer: B
CO poisoning comes from binding of CO to deoxyhemoglobin, giving a diamagnetic complex.
Deoxyhemoglobin contains high-spin Fe(II) (paramagnetic, S = 2). CO binds to the iron about 200 times more strongly than O2; as a strong-field σ-donor and π-acceptor it converts the iron to low-spin Fe(II), d6 with all electrons paired, so carboxyhemoglobin is diamagnetic. Hemoglobin blocked by CO cannot carry oxygen.
The product is not paramagnetic, so option A is wrong. CO inhibits cytochrome c oxidase in its reduced state, not the oxidised one, and that is not the main cause of poisoning. Each heme binds only one CO at its single open axial site, so 'two CO to heme' is wrong.
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