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JEE Main 2026 Apr 4 Shift 2, Chemistry Q13: Reactions of Various Orders

JEE Main2026Apr 4, Shift 2Chemistry
Q.

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?

  1. A

    The order of all the three reactions is same.

  2. 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.

  3. C

    The SI unit of rate constant of reaction 1 is s.

  4. D

    Thermal decomposition of HI on gold surface is an example of reaction 2.

Solution

Curve 1 is a straight line from [R] — characteristic of zero-order kinetics: .

Curves 2 and 3 are exponential decays (first-order or higher). Among them, curve 3 decays faster, so its rate constant is larger if both have the same order.

Now check each option:

(1) Wrong — curve 1 is zero-order while curves 2 and 3 are not, so orders differ.

(2) Correct — for the same order, the faster-decaying curve (3) has the larger rate constant.

(3) Wrong — SI unit of rate constant for a zero-order reaction is mol L s (concentration/time), not s.

(4) Wrong — thermal decomposition of HI on gold surface is a classic example of a zero-order reaction (curve 1), not curve 2.

Concept behind this question

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