When a reaction is progressing.

Options

A. The rate of the reaction goes on increasing
B. The concentration of the products goes on decreasing
C. The concentration of the reactants goes on decreasing
D. The reaction rate always remains constant

Answer

To solve the question "When a reaction is progressing," we need to analyze the statements provided regarding the behavior of reactants and products during a chemical reaction. Let's break down the solution step by step.

### Step 1: Understand the Reaction
Consider a general reaction:
\[ A + B \rightarrow C + D \]
Here, \( A \) and \( B \) are the reactants, and \( C \) and \( D \) are the products.

### Step 2: Analyze the Statements
We have four statements to evaluate:

1. **Statement 1**: The rate of the reaction goes on increasing.
- **Analysis**: This statement is incorrect. The rate of a reaction is dependent on the concentration of the reactants. As the reaction progresses, the concentration of the reactants decreases, leading to a decrease in the rate of the reaction.

2. **Statement 2**: The concentration of products goes on decreasing.
- **Analysis**: This statement is also incorrect. As the reaction proceeds, the products are formed from the reactants, so the concentration of products actually increases over time.

3. **Statement 3**: The concentration of reactants goes on decreasing.
- **Analysis**: This statement is correct. As the reactants are converted into products, their concentration decreases continuously throughout the reaction.

4. **Statement 4**: The reaction rate always remains constant.
- **Analysis**: This statement is incorrect. The reaction rate is not constant; it depends on the concentration of reactants, which decreases as the reaction proceeds, leading to a decrease in the rate.

### Step 3: Conclusion
From the analysis above, we can conclude that the correct statement regarding the progression of the reaction is:
- **Correct Answer**: The concentration of reactants goes on decreasing (Statement 3).