The amount of sample of Plutonium-32 which is remained after 99.4 days is 3.9 grams.
Remaining amount of any substance after the decay will be calculated by using the below equation:
N = N₀[tex](\frac{1}{2})^{\frac{T}{t}}[/tex], where
N = remained quantity = ?
N₀ = original quantity = 499.2g
T = total time = 99.4 days
t = half life time = 14.2 days
T/t = 99.4/14.2 = 7
On putting all these values in the above equation, we get
N = (499.2)(0.5)⁷
N = (499.2)(0.0078) = 3.9g
Hence remaining mass of Plutonium-32 is 3.9 g.
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