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Question:

In the reaction, A→product, −dAdt=K[A]. If we start with 10M of A, then after one natural life time, concentration of A decreased to :

10e M

5 M

2.5 M

10e2 M

Solution:

For first order reaction, C = Coe−Kt
At time t = 1/K
C = Co × e−K × 1/K = 10e−1 M
As Co = 10 M