The law of multiple proportions was proposed by: MCQ with Answer and Explanation

Explanation:
Reduction is gain of electrons or loss of oxygen. Here, CuO loses oxygen to form Cu, so CuO is reduced. H₂ gains oxygen to form H₂O, so H₂ is oxidized. This is a redox reaction. Oxidation and reduction occur simultaneously. Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons). In terms of oxygen, loss of O = reduction, gain of O = oxidation.

Explanation:
Enzymes are proteinaceous substances that act as biological catalysts, speeding up biochemical reactions in living organisms without being consumed. They are highly specific and work under mild conditions (pH, temperature). Examples: amylase breaks down starch, pepsin digests proteins. Inorganic catalysts are like Pt, Ni. Lipids are fats, not catalysts. Negative catalysts (inhibitors) slow reactions. Enzymes may be deactivated by high temperature or extreme pH.

Explanation:
Reverse osmosis (RO) uses pressure to force water through a membrane that blocks dissolved salts and impurities. Distillation uses boiling/condensation. Chlorination and ozonation are disinfection methods, not for desalination.