Valence factor of acids , bases and salts is different.
For an acid it is no. Of replaceable H+ ions.
For base it is the No. If OH- ions.
For salts it is the valency of any cation or anion present In it.
In the question the compound given s sodium benzoate which is a salt.
C6H5COONa
Which on dissociation gives :-
C6H5COONa -------> C6H5COO- + Na+
Hence here Valence factor =1