If the half-life of a radioactive atom is $2.3 \, days$,then its decay constant would be

The half-life of a radioactive isotope $X$ is $20$ years. It decays to another element $Y$,which is stable. The two elements $X$ and $Y$ were found to be in the ratio $1:7$ in a sample of a given rock. The age of the rock is estimated to be:

Half-life period of a sample is $15$ years. How long will it take to decay $96.875\%$ of the sample?

$A$ $280\, \text{day}$ old radioactive substance shows an activity of $6000\, \text{dps}$. $140\, \text{days}$ later, its activity becomes $3000\, \text{dps}$. What was its initial activity? ......... $\text{dps}$

If a radioactive substance decays $10 \%$ in every $16 \text{ hours}$, then the percentage of the radioactive substance that remains after $2 \text{ days}$ is

$A$ radioactive isotope $X$ with a half-life of $1.37 \times 10^9$ years decays to $Y$,which is stable. $A$ sample of rock from the moon was found to contain both the elements $X$ and $Y$ in the ratio of $1 : 7$. The age of the rock is