For a first order reaction $R \longrightarrow P$,the rate constant is $k$. If the initial concentration of $R$ is $[R_0]$,the concentration of $R$ at any time $t$ is given by the expression:

  • A
    $[R_0] e^{kt}$
  • B
    $[R_0] e^{-kt}$
  • C
    $[R_0](1 - e^{-kt})$
  • D
    $[R_0] + e^{-kt}$

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