For the reaction, PCl5(g)⇌PCl3(g)+Cl2(g), the position of equilibrium can be shifted to the right by:
LeChatelier′sprinciple states that changes in the temperature, pressure,
volume or concentration of a system will result in predictable and opposing
changes in the system in order to achieve a new equilibrium state.
If the reaction is endothermic, an increase in temperature will cause the forward reaction to occur, increasing the amounts of the products, and decreasing the amounts of reactants.
In an exothermic reaction, if you increase the temperature, then the number of products increases, and so you shift the balance at equilibrium back toward reactants, meaning there will be more reactants left at equilibrium.
since
PCl5(g)⇌PCl3(g)+Cl2(g) is endothermic reaction the position of the equilibrium shift towards right.
Hence the correct answer is option B.