In the given case:
Ea=209.5kJ mol−1=209500J mol−1
T=581K
R=8.314J K−1 mol−1
Now, the fraction of molecules of reactants having energy equal to or greater than activation energy is given as:
x=e−Ea/RT
lnx=−Ea/RT
logx=−Ea2.303RT
logx=−209500Jmol−12.303×8.314JK−1mol−1×581 =18.8323
Now, x= Anti log(18.8323)
=Antilog¯19.1677