The correct option is B High temperature
The given reaction is
2SO2(g)+O2(g)⇌2SO3(g)
We know, with increase in pressure the equilibrium will shift towards the side where fewer moles of the gases are present. So here at high pressure the rate of forward reaction will increase.
Since the reaction is exothermic, thus with increase in temperature the rate of backward reaction will increase. So high temperature is not favourable for the formation of SO3.
Decreasing SO3 concentration will shift the reaction towards forward direaction according to Le chatelier's principle. So it is favourable for SO3 formation.
Increasing reactant concentration also increases the formation of SO3 according to Le chatelier's principle only.