To denature a proteins means to subject the protein to a condition that makes the protein to stop functioning as usual. This is usually due to a permanent change in the structure or shape of the protein. A protein may be denatured by change in pH, heat of binding of other molecules to the protein molecule.
The final destination to where some of the electrons go to at the end of cellular respiration would be D. Oxygen. Assuming that this aerobic cellular respiration, the final electron acceptor is that of oxygen.
As acid rain is a mixture of pollutants and gasses. As rusting is a chemical reaction between oxygen and other gasses in the air alongside a material and a liquid. I would say they are both similar and that acid rain would speed the process of rusting/aid the process.
