Match List-I (unit of the rate constant) with List-II (order of the reaction).
| List-I | List-II |
| (A) mol L−1 s−1 | (p) First order |
| (B) s−1 | (q) Zero order |
| (C) L mol−1 s−1 | (r) Third order |
| (D) L2 mol−2 s−1 | (s) Second order |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-q, B-p, C-s, D-r
For a reaction of order n, rate = k[A]n, so the unit of k is the unit of rate divided by (unit of concentration)n:
\( \displaystyle k=\frac{\mathrm{mol\,L^{-1}\,s^{-1}}}{(\mathrm{mol\,L^{-1}})^{n}}=(\mathrm{mol\,L^{-1}})^{1-n}\,\mathrm{s^{-1}} \)
(A) mol L−1 s−1 — This matches (q) Zero order. With n = 0, k has the same unit as the rate.
(B) s−1 — This matches (p) First order. With n = 1, the concentration units cancel and only s−1 is left.
(C) L mol−1 s−1 — This matches (s) Second order. With n = 2, k = (mol L−1)−1 s−1.
(D) L2 mol−2 s−1 — This matches (r) Third order. With n = 3, k = (mol L−1)−2 s−1.
NCERT (2026-27 edition):
3.2.3 Order of a Reaction – “… Taking SI units of concentration, mol L–1 and time, s, the units of k for different reaction order are listed in Table 3.3”
Table 3.3: Units of rate constant
