Question

Chemical used for preserving jam and jelly
A.Sodium chloride
B.Acetic acid
C.Citric acid
D.Sodium benzoate

Answer 1

Jams and jellies are slightly acidic foods and their pH favors the microbial activity. The preservative we use, must change the pH of the product in order to protect it from getting spoiled.

Complete step by step answer:
Antimicrobial activity is achieved by the inhibition in the enzymatic system of the microbial cells, affecting various systems in the cells by affecting citric acid cycle, acetic acid metabolism and oxidative phosphorylation. The antimicrobial activity is pH dependent. Inhibition of the enzymatic system of microbial cells is maximum in the pH range of $2.5$ to $4.0$ . So, the role of the preservative used is to decrease the pH of the foods in order to inhibit the microbial activity and maintain the food products in a consumable state.
Sodium benzoate reduces the pH of the solution as, under the conditions existing in the food products, like jams and jellies, it is converted into benzoic acid.
Thus sodium benzoate is generally used as a preservative in products made of fruit extracts like jams, jellies, fruit juices, pickles, ketchup, salad dressings and others.

Hence option D is correct.
Note:
Sodium benzoate is a class 2 preservative. The use of class 2 preservatives is said to be harmful and thus they shall be added only to specific products and in a limited specified concentration so as to reduce the side effects on the consumer.
Benzoic acid and its salts are used as antimicrobial agents. They are highly effective against bacteria (bacteriostatic) and yeast (fungi static). Benzoic acid is rarely used as preservative due to low solubility in water and therefore its salts, like sodium benzoate, are used.