The rate constant for a reaction is $3.5\, mol^{-1}\, L\, s^{-1}$. The order of the reaction is:

Second

The correct answer is Option (3) → Second

The units of the rate constant (k) depend on the order of the reaction (n):

$\text{Units of } k = \text{(concentration)}^{1-n} \cdot \text{time}^{-1}$

Given:

• $k = 3.5\ \mathrm{mol^{-1} L s^{-1}}$

Compare with the general unit formula:

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