Low pressure is favourable for those reversible reactions in which there is ………… in the number of molecules.

Explanation

To solve the question regarding the effect of low pressure on reversible reactions, we can follow these steps:

### Step 1: Understand the Concept of Equilibrium
Reversible reactions can reach a state of equilibrium where the rate of the forward reaction equals the rate of the reverse reaction. The position of this equilibrium can be affected by changes in conditions such as pressure.

**Hint:** Consider how changes in pressure affect the concentration of gaseous reactants and products.

### Step 2: Apply Le Chatelier's Principle
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