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Question:

For the elementary reaction M→N, the rate of disappearance of M increases by a factor of 8 upon doubling the concentration of M. The order of the reaction with respect to M is:

1

2

4

3

Solution:

The correct option is B

r1=k[m]n
r2=k[2m]n

Also,
r1/r2 = 1/8

r1/r2 = [m]n/[2m]n

⇒ 1/8 = (1/2)n

⇒ n = 3

Hence, option B is correct.