The correct option is C Adding F2
According to the Le Chatlier's principle, A system in chemical equilibrium changes towards a new equilibrium when subjected to a change in pressure, temperature, volume, or concentration. The equilibrium shift partly counteracts the change that was applied to the system initially.
Here, as the concentration of F2 is increased, the equilibrium shifts towards the opposite side resulting in the formation of ClF3
Also, as temperature is increased and the reaction is exothermic, the equilibrium constant value decreases.