If the decay or disintegration constant of a radioactive substance is $\lambda$,then its half-life and mean life are respectively $(log_e 2 = \ln 2)$.

• A
  $\frac{1}{\lambda}$ and $\frac{log_e 2}{\lambda}$
• B
  $\frac{log_e 2}{\lambda}$ and $\frac{1}{\lambda}$
• C
  $\lambda log_e 2$ and $\frac{1}{\lambda}$
• D
  $\frac{\lambda}{log_e 2}$ and $\frac{1}{\lambda}$