when a 2 litre reaction vessel in which 15 grammes of pcl5 had been placed and mantained at 250 degrees celsius until equilibrium was established and found that 364grammes of cl2 remained in the vessel .find the Kc at this temperature and reaction

Let me get this straight: you started with 15g of a compound, decomposed some of it, and the mass of one of the components is 364grams? That is really cool. Recheck your data.