Read the passage carefully and answer the Questions.

The concentration dependence of the rate of a reaction is called the differential rate equation. It is not always convenient to determine the instantaneous rate, as it is measured by calculating the slope of the tangent at point 't' in the concentration vs time plot. This makes it difficult to determine the rate and hence the order of the reaction. This difficulty is overcome by integrating the differential rate equation. This integrated rate equation gives a direct relation between concentrations at different times and the rate constant. The integrated rate equations are different for the reactions having different reaction orders.

The rate constant of a reaction is $2.1\, mol\, L^{-1}s^{-1}$. What is the order of the reaction?

Zero order

The correct answer is Option (1) → Zero order

The order of a reaction can be determined from the units of the rate constant (k).

Given:

$k = 2.1 \ \text{mol L}^{-1}\text{s}^{-1}$

For different orders:

• Zero order: $\text{mol L}^{-1}\text{s}^{-1}$
• First order: $\text{s}^{-1}$
• Second order: $\text{L mol}^{-1}\text{s}^{-1}$
• Third order: $\text{L}^2\text{mol}^{-2}\text{s}^{-1}$

Since the units match those of a zero-order reaction.