`underline("Catalyst is a substance which alters ")`the equilibrium constant of reaction

Explanation

### Step-by-Step Solution:

1. **Understanding the Definition of a Catalyst**:
A catalyst is defined as a substance that increases the rate of a chemical reaction without being consumed in the process. It achieves this by providing an alternative reaction pathway with a lower activation energy.

2. **Equilibrium Constant**:
The equilibrium constant (K) of a reaction is a value that expresses the ratio of the concentration of products to the concentration of reactants at equilibrium. It is determined by the nature of the reactants and products and the temperature of the system.

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