Radioactive decay follows first order kinetics. Consider the following radioactive decay in a 45 L closed vessel at 300 K.
${}_{83}\text{B}{\text{i}}^{211}\stackrel{ }{\to }{}_{81}\text{Tl}^{207}+{}_2\text{He}^4$
The reaction starts with 4 mol of  ${}_{83}\text{Bi}^{211}$. The pressure (in atm) developed after 20.4 minutes from the start is_____. [Given  $t_{\frac{1}{2}}=5.1\min$; Use ln2 = 0.7, R = 0.08 L atm $mo{l}^{-1} K^{-1}]$