Answer
$0.181 d^{-1}$
Work Step by Step
We can find the decay constant for radon as follows:
$T_{\frac{1}{2}}=\frac{\ln 2}{\lambda}$
This can be rearranged as:
$\lambda=\frac{\ln 2}{T_{\frac{1}{2}}}$
We plug in the known values to obtain:
$\lambda=\frac{\ln 2}{3.82d}$
$\lambda=0.181 d^{-1}$
