For the gaseous reactionas per Lechatelier's principle which of the following changes favour forward reaction yielding more sulphur trioxide ?A) Adding more oxygen           B) Removing sulphur trioxide   C) Applying high pressure   D) presence of catalyst

Addition of SO2 and O2(or) removal of SO3  favour forward reaction.Since the formation of SO3 is exothermic it is favoured at low temperatureSince the formation of SO3 involves decrease in volume or gaseous moles it is  favoured at high pressureA, B, C are correctA catalyst never influences the position of equilibrium state.