What type of allergen is sulphites?

Sulphites are classified as a preservative, which is why this option is the correct answer. They are often used in food preservation to prevent spoilage and maintain the appearance of food products. Sulphites can be found in various foods and beverages, including dried fruits, wines, and some processed foods, where they serve to maintain freshness and inhibit microbial growth.

The other options are specific types of allergens that pertain to particular categories of food. Gluten is a protein found in wheat and is associated with celiac disease or gluten intolerance. Dairy refers to milk and milk products, which can cause allergic reactions in individuals with dairy allergies. Nuts are another common allergen, known for their potential to provoke severe allergic reactions. However, neither gluten, dairy, nor nut allergies relate to the role of sulphites as preservatives in food. This distinction highlights the unique classification of sulphites as a preservative rather than an allergen associated with specific food groups.