Q1 Why there is no warning label for a reducing agent. Is it because of how oxidation and reduction always happened together, thus an oxidizing agent is reducing when compared with a stronger oxidizing agent? Q2 What are the possible reasons that nature failed to make enzymes that bind to Al or Hg and utilize them, thus making them classified as toxic metals because of how they can disrupt metalloenzymes normal functiosn by displacing the metals away from the active site or bind to them (or their ligands) and inhibit their actions For example, we know Hg has a strong affinity for Se and S atoms. Since there are 2 amino acids that contains sulfur (methionine and cysteine), and form what I learnt in the biometallic chemistry course that most metal ions are bound in enzymes to prevent the free ion from wrecking havoc to other biological components while allowing the metal to carry out important reactions such as hydrogenation, nitrogen fixing, respiration etc., and that mercury is quite widespread in the environment. Shouldn't it would be plausible for nature to have discovered e.g. sulfur rich ligands binding to Hg and than resulting in a enzyme that can functionalise mercury to carry out biological process, thus making mercury essential to that organism in question? As of today, there are non known examples of organisms or enzymes found that utilize mercury. what are the possible reasons, using what we know in the scientific consensus in the biology (evolution, genetics, biochemistry) and chemistry (physical, inorganic, organic, analytical, biochem) domain that make it highly unlikely for an enzyme that can utilize mercury (or any toxic metals in general) to be evolved or naturally produced?