Which may be added to one litre of water to act a buffer ?

(4)  Acetic acid is weak acid ,it forms salt CH3COONa  with strong base NaOH.Hence it is a acidic buffer.HC2H3O2   +   NaOH    →   C2H3O2Na  +  H2O           1                  0.5                       0                     0            0.5              0                          0.5                0.5   This solution contains weak acid + its salt with strong base and thus acts as acidic buffer.