$A$ radio isotope has a half-life of $75\, \text{years}$. The fraction of the atoms of this material that would decay in $150\, \text{years}$ will be...........$\%$

At time $t = 0$,$N_1$ nuclei of decay constant $\lambda_1$ and $N_2$ nuclei of decay constant $\lambda_2$ are mixed. The decay rate of the mixture is:

The relation between half-life $(T)$ and decay constant $(\lambda)$ is

$90\%$ of a radioactive sample is left undecayed after time $t$ has elapsed. What percentage of the initial sample will decay in a total time $2t$ : ..............$\%$

$A$ and $B$ are two radioactive elements. The mixture of these elements shows a total activity of $1200 \text{ disintegrations/minute}$. The half-life of $A$ is $1 \text{ day}$ and that of $B$ is $2 \text{ days}$. What will be the total activity after $4 \text{ days}$? Given,the initial number of atoms in $A$ and $B$ are equal.

$A$ radioactive element decays to form a stable nuclide. The rate of decay of the reactant $\left( \frac{dN}{dt} \right)$ will vary with time $(t)$ as shown in which figure?