Which of the following is the most commonly used food preservative?

Sodium benzoate is a preservative. As a food additive, sodium benzoate has the E number E-211. It is bacteriostatic and fungistatic under acidic conditions.
It is most widely used in acidic foods such as salad dressings (vinegar), carbonated drinks (carbonic acid), jams and fruit juices (citric acid), pickles (vinegar), and condiments.