In: Chemistry
(a) From the graph, the percentage of the sample after 130 days is \(30 \%\)
The mass of the initial sample is \(5.25 \mathrm{~g}\).
So, calculate the mass of original iridium-192 after 130 days as follows:
mass of original \(=30 \% \times\) mass of the initial sample
$$ \begin{aligned} &=\frac{30}{100} \times(5.25 \mathrm{~g}) \\ &=1.575 \mathrm{~g} \\ &\cong 1.58 \mathrm{~g} \end{aligned} $$
(b) From the graph, the half-life at \(50 \%\) sample is about 75 days.
(c) Two-third of the sample decay means one-third remains, that is \(33 \%\). Then time is 120 days from graph.