$A$ radioactive nucleus decays by two different processes. The half-life for the first process is $10 \ s$ and that for the second is $100 \ s$. The effective half-life of the nucleus is close to $..... \ s$.

The half-life of ${ }_{84}^{209} Po$ is $103 \text{ years}$. The time it takes for a $100 \text{ g}$ sample of ${ }_{84}^{209} Po$ to decay to $3.125 \text{ g}$ is

In the figure,$X$ represents time and $Y$ represents the activity of a radioactive sample. Then the activity of the sample varies with time according to the curve:

The half-life of a radioactive sample is $T$. What fraction of the substance will remain after a time $T/2$?

The curve between the activity $A$ of a radioactive sample and the number of active atoms $N$ is

The half-life of a radioactive isotope $x$ is $50$ years. It decays to another element $y$ which is stable. The two elements $x$ and $y$ were found to be in the ratio of $1 : 7$ in a sample of a given rock. The age of the rock was estimated to be ........... $years$.