The disintegration constant of radium with a half-life of $1600 \ years$ is:

The half-life of a radioactive substance is $120$ days. After $480$ days,the amount of $4 \ g$ of the substance remaining will be: (in $g$)

The rate constant for a radioactive decay reaction is $\lambda$. The average life is represented by:

The amount of $_{53}I^{128}$ $(t_{1/2} = 25 \ min)$ remaining after $75 \ min$ is:

After $2 \, \text{hours}$,the amount of a certain radioactive substance reduces to $1/16^{th}$ of the original amount (the decay process follows first-order kinetics). The half-life of the radioactive substance is $...... \, \text{min}$.

If $2.0 \ g$ of a radioactive isotope has a half-life of $20 \ hr$,the half-life of $0.5 \ g$ of the same substance is ........ $hr$.