For the reaction, 

$2{\mathrm{SO}}_2\left(g\right)+{\mathrm{O}}_2\left(g\right)\rightleftharpoons 2{\mathrm{SO}}_3\left(g\right)\mathrm{\Delta }{H}^{\circ }<0$ 

Which change(s) will increase the fraction of ${\mathrm{SO}}_3 \left(\mathrm{g}\right)$ in the equilibrium mixture?
(P) Increasing the pressure
(Q) Increasing the temperature
(R) Adding a catalyst