While filling electrons in ${\mathrm{\pi }}_{2{\mathrm{p}}_{\mathrm{x}}}$ and ${\mathrm{\pi }}_{2{\mathrm{p}}_{\mathrm{y}}}$ the electronic configuration rules that one to be followed is

• ${\mathrm{\pi }}_{2{\mathrm{p}}_{\mathrm{x} }}\mathrm{and} {\mathrm{\pi }}_{2{\mathrm{p}}_{\mathrm{y}}}$molecular orbitals are degenerate orbitals i.e., they have the same energy level
• As they have the same energy level, sub-levels in the p-orbital would be have filled first. 
• Only if all 3 sub-levels in p-orbitals are half – filled, pairing starts to have. This is Hund’s rule
• In addition to that, each orbital can have only 2 electrons and these two electrons must have opposite spin. This is Pauli’s rule
• Thus, Pauli’s rule and Hund’s rule must be followed while filling electrons in  orbitals

Hence, Option (C) Both Pauli’s and Hund's rule is the correct answer