Q28 / 90 · JEE Main 2018 (16 Apr Online) · Chemistry

If 50 % of a reaction occurs in 100 second and 75 % of the reaction occurs in 200 second, the order of this reaction is:

  • A
    2
  • B
    3
  • C
    Zero
  • Correct answer
    D
    1

Solution

50% of a reaction occurs in 100 second and 75% of the reaction occurs in 200 second, the order of this reaction is 1.

Let the initial reactant concentration is 1 M.

In the first 100 seconds, reactant concentration is reduced to 50% or 1×50100​=0.5 M.

In the second 100 seconds (total 200 seconds from start), reactant concentration is reduced to 100−75=25% or  1× 25100​ =0.25 M..

Thus, we observe that after each 100 second period, the reactant concentration is reduced to one half. Hence, 100 seconds is the half-life period and is independent of reactant concentration. This is characteristic of the first-order reaction.

Figure

First-order reaction as the half-life is constant.

Hence, the correct answer is option: 'D'.

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