A reaction proceeds through the formation of an intermediate B in a unimolecular reaction \[A\xrightarrow{{{k_a}}}B\xrightarrow{{{k_b}}}C\]
The integrated rate law for this reaction is

A. $$\left[ A \right] = {\left[ A \right]_0}{e^{ - {k_a}t}}$$

B. $$\left[ A \right] = {\left[ A \right]_0}\left( {{e^{ - {k_a}t}} - {e^{ - {k_b}t}}} \right)$$

C. $$\left[ A \right] = \frac{{{{\left[ A \right]}_0}}}{2}\left( {1 + \frac{{{k_a}{e^{ - {k_b}t}} - {k_b}{e^{ - {k_a}t}}}}{{{k_a} - {k_b}}}} \right)$$

D. $$\left[ A \right] = {\left[ A \right]_0}\left( {1 + {e^{ - {k_a}t}} - {e^{ - {k_b}t}}} \right)$$

Answer: Option A