In a reaction,
`aA+bBrarrcC+dD`
rate `=-1/a(d[A])/(dt)` , the - ve sign in it represents

Options

A. The rate of reaction increases with time
B. The rate is negative for the reaction
C. The concentration of the reactant 'A' decreases during the reaction
D. The concentration of reactant 'A' increases in the reaction

Answer

To solve the question regarding the negative sign in the rate expression for the reaction \( aA + bBr \rightarrow cC + dD \), we will analyze the meaning of the rate of reaction and the role of reactants and products.

### Step-by-Step Solution:

1. **Understanding the Rate Expression**:
The rate of reaction is given by the expression:
\[ \text{Rate} = -\frac{1}{a} \frac{d[A]}{dt} \]
Here, \([A]\) represents the concentration of reactant A, and \(d[A]/dt\) is the change in concentration of A with respect to time.

2. **Significance of the Negative Sign**:
The negative sign in the rate expression indicates that the concentration of reactant A is decreasing over time. In chemical reactions, reactants are consumed to form products. Therefore, as the reaction progresses, the concentration of A diminishes.

3. **Graphical Interpretation**:
If we were to plot the concentration of A against time, we would observe a downward slope, indicating that the concentration of A is decreasing. The negative sign in the rate expression mathematically represents this decrease.

4. **Conclusion**:
The negative sign is not an indication of the rate being negative or that the reaction is unfavorable; rather, it signifies that the concentration of the reactant A is decreasing as the reaction proceeds. Thus, the correct interpretation is that the concentration of reactant A decreases during the reaction.

### Final Answer:
The negative sign in the rate expression represents that the concentration of reactant A decreases during the reaction.

---