Define 'order of a reaction'.

Explanation

### Step-by-Step Text Solution

**Step 1: Definition of Order of Reaction**
The order of a reaction is defined as the sum of the powers of the concentration of the reactants in the rate law expression.

**Step 2: Understanding Rate Law Expression**
The rate law expression for a reaction can be represented as:
\[ \text{Rate} = k [A]^x [B]^y \]
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