In which of the following gaseous phase reversible reactions, the product yield cannot be increased by the application of high pressure ?
A. N2 + O2 ⇌ 2NO
B. PCl3 + Cl2 ⇌ PCl5
C. N + 3H2 ⇌ 2NH3
D. 2SO2 + O2 ⇌ 2SO3