The average life T and the decay constant $\mathrm{\lambda }$ of a radioactive nucleus are related as 

• A

  $\mathrm{T\lambda }=1$

• B

  $\mathrm{T}=\frac{0.693}{\mathrm{\lambda }}$

• C

  $\frac{\mathrm{T}}{\mathrm{\lambda }}=1$

• D

  $\mathrm{T}=\frac{\mathrm{c}}{\mathrm{\lambda }}$