The correct options are
B 0.5 mol of Hg deposited
D 0.125 mol of O2 produced
To deposit one mole of mercury, one mole of electrons is required.
Hg++e−→Hg
Hence 0.5 mole of electron will deposit 0.5 mole of mercury.
To deposit one mole of oxygen, four moles of electrons is required.
4OH−→2H2O+O2+4e−
Hence 0.5 mole of electrons will deposit 0.125 mole of oxygen.