Consider the given graph showing variation of reactant concentration with time. Three different reactions were started with identical initial concentration of reactants. Which of the following statement is correct?
(A)The order of all the three reactions is same.
(B)The rate constant of reaction 3 is larger than the rate constant of reaction 2 if the order of reaction is same for both.✓ Correct
(C)The SI unit of rate constant of reaction 1 is s−1.
(D)Thermal decomposition of HI on gold surface is an example of reaction 2.
Answer: (B)
Solution
The three curves start from the same initial concentration but fall off differently, so their kinetics are not identical. Curve 1 declines almost linearly, the mark of a zero-order reaction, whose rate constant has units of molL−1s−1 rather than s−1. Thermal decomposition of HI on a gold surface is the standard zero-order example and therefore matches curve 1, not curve 2. Comparing the steeper curves 2 and 3, a faster fall in concentration means a faster reaction, so if the two share the same order the one that drops more steeply has the larger rate constant: for the same order the rate constant of reaction 3 is larger than that of reaction 2.
JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Single correct option
