Order of a chemical reaction.

Explanation

**Step-by-Step Solution:**

1. **Definition of Order of a Chemical Reaction:**
The order of a chemical reaction is defined as the sum of the powers of the concentration terms in the rate law expression for that reaction. It indicates how the rate of reaction depends on the concentration of reactants.

2. **Understanding Rate Law:**
The rate law for a chemical reaction can be expressed in the form:
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