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