$A$ certain nuclide has a half-life period of $30 \ minutes$. If a sample containing $600$ atoms is allowed to decay for $90 \ minutes$,how many atoms will remain?

The half-life of $_6C^{14}$ if its decay constant $k$ or $\lambda$ is $2.31 \times 10^{-4} \ yr^{-1}$ is:

If the quantity of a radioactive element is doubled,then its rate of disintegration per unit time will be

The half-life period of a radioactive material is $15 \ minutes$. What $\%$ of radioactivity of that material will remain after $45 \ minutes$?

$A$ radioactive isotope having $t_{1/2} = 3 \ days$ was measured after $12 \ days$. If $3 \ g$ of the isotope remains in the container,what was the initial weight of the isotope (in $g$)?

Half-life of a radioactive substance which disintegrates by $75\%$ in $60 \ min$ will be ......... $min$.