Which of the following is a characteristic of a reversible reaction ?

Options

A. it never proceeds to completion
B. it can be influenced by a catalyst
C. it proceeds only in forward direction
D. number of moles of reactants and products are equal

Explanation

To determine the characteristic of a reversible reaction, we need to analyze the provided statements one by one.

### Step-by-Step Solution:

1. **Understanding Reversible Reactions**:
- Reversible reactions are those in which the conversion of reactants to products and products back to reactants occurs simultaneously. This means that both the forward and backward reactions can take place.

2. **Analyzing the Statements**:
- **Statement 1**: "It never proceeds to completion."
- This statement is true. In reversible reactions, the system reaches an equilibrium state where the concentrations of reactants and products remain constant over time. Therefore, the reaction does not go to completion.

- **Statement 2**: "It can be influenced by a catalyst."
- This statement is false. While a catalyst can speed up the rate at which equilibrium is reached, it does not change the position of the equilibrium or the thermodynamic properties of the reaction. Thus, it does not influence the nature of the reversible reaction itself.

- **Statement 3**: "It proceeds only in the forward direction."
- This statement is also false. Reversible reactions can proceed in both the forward and backward directions, meaning that reactants can form products and products can revert to reactants.

- **Statement 4**: "The number of moles of reactants and products are equal."
- This statement is incorrect. The number of moles of reactants and products in a reversible reaction are not necessarily equal. This equality can only be true under specific conditions, such as in a closed system.

3. **Conclusion**:
- Based on the analysis, the only characteristic of a reversible reaction from the provided statements is that it never proceeds to completion.

### Final Answer:
The characteristic of a reversible reaction is: **It never proceeds to completion.**