Oxidant is a substance in which the oxidation number of one of the atoms ……………….and reductant is a substacne in which oxidation number of one of atoms ……………..

Answer

To answer the question regarding oxidants and reductants, we need to understand the definitions and the changes in oxidation numbers associated with these substances.

### Step-by-Step Solution:

1. **Definition of Oxidant**: An oxidant, also known as an oxidizing agent, is a substance that causes oxidation in another substance. This means that the oxidant itself undergoes a reduction process, where its oxidation number decreases.

**Fill in the blank**: "Oxidant is a substance in which the oxidation number of one of the atoms **decreases**."

2. **Definition of Reductant**: A reductant, or reducing agent, is a substance that causes reduction in another substance. In this case, the reductant itself undergoes an oxidation process, which means its oxidation number increases.

**Fill in the blank**: "Reductant is a substance in which the oxidation number of one of the atoms **increases**."

### Final Answer:
- Oxidant is a substance in which the oxidation number of one of the atoms **decreases**.
- Reductant is a substance in which the oxidation number of one of the atoms **increases**.