Oxidation is defined as the loss or removal of electrons from a substance. A common mnemonic device used to remember this is "OIL RIG", which stands for "Oxidation Is Loss", "Reduction Is Gain" (of electrons). When a substance is oxidized, its oxidation number increases, indicating a loss of negatively charged electrons.

A. hydrolysed and D. hydrated: Hydrolysis is a chemical process involving the splitting of a molecule by the addition of water, while hydration is the addition of water molecules to a substance. These processes are not the general definition of what happens to electrons during oxidation reactions.

C. added: The addition or gain of electrons is the definition of a reduction reaction, which occurs simultaneously with oxidation in a redox reaction.

The correct answer is option B - removed