Question

The addition of oxygen to a substance is called __________ whereas removal of oxygen is _________. (Fill in the following blanks with suitable words).

Answer 1

Hint: When a substance reacts with oxygen and oxygen gets added to it, the substance is said to be oxidized and the reaction is called an oxidation reaction. On the other hand, when oxygen is removed from the substance, the substance is said to be reduced and the reaction is called a reduction reaction.

Complete answer:
When iron combines with oxygen from the air, it forms an iron oxide that is also known as rust. Since oxygen is adding to the iron metal, the iron is said to be oxidized. And the chemists named such a reaction in which oxygen combines with a substance as oxidation.
The reverse of such reactions, leading to the removal of oxygen from the compound is known as reduction. Also, in earlier times, chemists use another definition to describe a reduction reaction as the gain of the hydrogen atom.
The substance which acts as a source of oxygen or oxidizes another substance is called an oxidizing agent. While the substance which takes up oxygen from another substance is known as a reducing agent.
For example:
\[\begin{align}
  & 2\text{Mg(s)}+{{\text{O}}_{\text{2}}}\text{(g)}\to 2\text{MgO(s) }\!\![\!\!\text{ Oxidation }\!\!]\!\!\text{ } \\
 & \text{MgO(s)}+\text{C(s)}\to \text{Mg(s)}+\text{CO(g) }\!\![\!\!\text{ Reduction }\!\!]\!\!\text{ } \\
\end{align}\]
The first reaction is an oxidation reaction where Mg is getting oxidized to MgO and in the second reaction, reduction of MgO is taking place.
Hence, the correct answer would be:
The addition of oxygen to a substance is called oxidation whereas removal of oxygen is reduction.

Note:
Later on in the field of chemistry, when electrons were discovered the definition of oxidation and reduction was modified. Oxidation is the loss of electrons during a reaction by a molecule, atom, or ion and the opposite process is called reduction, which occurs when there is a gain of electrons by the substance.