Answer: 0.125 grams
Explanation:
Radioactive decay follows first order kinetics.
Half-life of give isotope = 20 minutes
\(\lambda =\frac{0.693}{t_{\frac{1}{2}}}=\frac{0.693}{20}=0.03465min^{-1}\)
\(N=N_o\times e^{-\lambda t}\)
N = amount left after time t= ?
\(N_0\) = initial amount = 1.0 g
\(\lambda\) = rate constant
t= time = 1 hour = 60 min
\(N=1.0\times e^{- 0.03465mi^{-1}\times 60min}\)
N=0.125g
Thus amount left after 1 hour is 0.125 grams
