Rate at particular moment of time is the correct answer for the term "instantaneous reaction".

Explanation:

An instantaneous reaction refers to a reaction that occurs in an extremely short period of time. It is a reaction that takes place at a particular moment in time, and its rate can be determined at that specific instant. The rate of a reaction is defined as the change in concentration of a reactant or product per unit time.

Rate at particular moment of time:

The rate of a reaction at a particular moment in time can be determined by measuring the change in concentration of a reactant or product over a very small time interval. This can be done by measuring the concentration of a reactant or product at two closely spaced time points and calculating the difference in concentration divided by the time interval. The smaller the time interval, the more accurate the determination of the instantaneous rate.

Example:

For example, consider the reaction A → B. The rate of this reaction at a particular moment in time can be determined by measuring the concentration of A and B at that instant. If the concentration of A is decreasing rapidly and the concentration of B is increasing rapidly, it indicates a high rate of the reaction at that moment. On the other hand, if the concentrations of A and B are not changing significantly, it indicates a low rate of the reaction at that moment.

Importance:

Determining the rate of a reaction at a particular moment in time is important in understanding the kinetics of a reaction. It helps in studying the reaction mechanism, identifying the factors that affect the rate of the reaction, and predicting the behavior of the reaction under different conditions.

Conclusion:

In conclusion, an instantaneous reaction refers to a reaction that occurs at a particular moment in time. The rate of this reaction at that moment can be determined by measuring the change in concentration of a reactant or product over a very small time interval. This instantaneous rate helps in understanding the kinetics of the reaction and predicting its behavior.