In a first order reaction,the concentration of the reactant is reduced to $25\%$ in one hour. The half-life period of the reaction is:

  • A
    $2 \ hr$
  • B
    $4 \ hr$
  • C
    $1/2 \ hr$
  • D
    $1/4 \ hr$

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The following is a first-order reaction:
$N_2O_5 \text{ (solution)} \rightarrow 2 NO_2 \text{ (solution)} + \frac{1}{2} O_2 \text{ (g)}$
In this reaction,$CCl_4$ is the solvent. The rate constant is $k = 5.0 \times 10^{-4} \ s^{-1}$. The initial concentration of $N_2O_5$ is $0.25 \ mol \ L^{-1}$.
$(i)$ What will be the initial rate of reaction?
$(ii)$ Calculate the half-life $(t_{1/2})$.
$(iii)$ How much time is required to complete $75\%$ of the reaction?
$(iv)$ Calculate the concentration of $N_2O_5$ and $NO_2$ after $30 \ min$.

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Which of the following graphs represent a first order reaction ($a =$ initial concentration of reactant,$x =$ concentration of reactant consumed,$t =$ time)?

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