Answer
0.197 M
Work Step by Step
Given: $\Pi= 4.85\,atm$
T= 300 K and we know that $R= 0.0821 L\,atm\,mol^{-1}K^{-1}$
Recall: $\Pi= cRT$ or $c=\frac{\Pi}{RT}$
Substituting the values:
$c= \frac{4.85\,atm}{0.0821\,L\,atmK^{-1}mol^{-1}\times300K}$
Result: Molarity c= 0.197 M