The graph between the instantaneous concentration $(N)$ of a radioactive element and time $(t)$ is

A certain radioactive material can undergo three different types of decay, each with a different decay constant $\lambda_1$, $\lambda_2$ and $\lambda_3$ . Then the effective decay constant is

$16\, gm$ sample of a radioactive element is taken from Bombay to Delhi in $2\, hour$ and it was found that $1\, gm$ of the element remained (undisintegrated). Half life of the element is

Half life of a radio-active substance is $20\, minutes$. The time between $20\%$ and $80\%$ decay will be ........... $minutes$

A radioactive sample disintegrates via two independent decay processes having half lives $T _{1 / 2}^{(1)}$ and $T _{1 / 2}^{(2)}$ respectively. The effective half- life $T _{1 / 2}$ of the nuclei is

The half-life of a radioactive element $A$ is the same as the mean-life of another radioactive element $B.$ Initially both substances have the same number of atoms, then