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The count rate for $10\ g$ of radioactive material was measured at different times and this has been shown in the graph with scale given. The half life of the material and the total count in the first half value period respectively are
$4\ hours$ and $9000$ (approx.)
$3\ hours$ and $14100$ (approx.)
$3\ hours$ and $235$ (approx.)
$10\ hours$ and $150$ (approx.)
Solution
From graph $\mathrm{T}_{\mathrm{H}}=$ The time in which activity (count rate) becomes half
$=3 \mathrm{h}=180 \mathrm{\,min}$
Approximate mean disintegration rate in first half life period
$=\frac{100+50}{2}=75 $ decay/minute
$\therefore$ Total count in first half value period $=75 \times 180=13500$
But the total no. of disintegrations are slightly greater than $13500 .$
Hence, the answer is $3 \mathrm{h}$ and $14100$ (approx)
