The rate constant of a reaction is given as k = 3.3 × 10–5 L mol–1 s–…

The correct answer is Option (1) → Second order

The rate of a reaction is the change in concentration per unit time, so its unit is always mol L⁻¹ s⁻¹. For a reaction of order n:

    \( \displaystyle \mathrm{Rate}=k[\mathrm{A}]^n,\quad k=\frac{\mathrm{Rate}}{[\mathrm{A}]^n} \)

    \( \displaystyle \text{Unit of }k=\frac{\mathrm{mol\,L^{-1}\,s^{-1}}}{(\mathrm{mol\,L^{-1}})^n}=(\mathrm{mol\,L^{-1}})^{1-n}\,\mathrm{s^{-1}} \)

Putting in the common orders:

    \( \displaystyle \text{Zero order }(n=0)\text{: }\mathrm{mol\,L^{-1}\,s^{-1}} \)

    \( \displaystyle \text{First order }(n=1)\text{: }\mathrm{s^{-1}} \)

    \( \displaystyle \text{Second order }(n=2)\text{: }\frac{\mathrm{mol\,L^{-1}\,s^{-1}}}{\mathrm{mol^2\,L^{-2}}}=\mathrm{mol^{-1}\,L\,s^{-1}} \)

    \( \displaystyle \text{Third order }(n=3)\text{: }\mathrm{mol^{-2}\,L^2\,s^{-1}} \)

The given rate constant, 3.3 × 10⁻⁵ L mol⁻¹ s⁻¹, has the unit L mol⁻¹ s⁻¹, which is the same as mol⁻¹ L s⁻¹. So the reaction is of second order.

NCERT (2026-27 edition):
Order of a Reaction

Note: The same/similar question has been asked in different years by NTA as per the details given below: