# In which of the following reactions $H_2O_2$ acts as a reducing agent ?
( A ) $Na_2SO_3 + H_2O_2 \to Na_2SO_4 + H_2O$
( B ) $PbS + 4H_2O_2 \to PbSO_4 + 4H_2O$
( C ) $NaNO_2 + H_2O_2 \to NaNO_3 + H_2O$
( D ) $Ag_2O (moist) + H_2O_2 \to 2Ag + H_2O + O_2$