Potassium meta-bisulphite is commonly used as a food preservative, particularly in the preservation of fruit juices. It helps in preventing the growth of microorganisms such as bacteria and yeast, thus extending the shelf life of the juice. This compound acts as an antioxidant, preventing oxidation and spoilage of the juice.

Although it can be used in other food products as well, such as squash, tomato ketchup, and pickles, the most suitable option is fruit juices. Fruit juices are prone to spoilage due to their high sugar content, making them an ideal environment for microorganisms to thrive. Therefore, the addition of potassium meta-bisulphite helps in maintaining the quality and freshness of the fruit juice for a longer period.

Alert - Correct answer should be 4. Potassium meta-bisulphite is commonly used as a food preservative, particularly in the preservation of pickles. It helps in preventing the growth of microorganisms and maintaining the freshness of pickles.