Explanation:

In India, the FPO (Fruit Products Order) mark is a mandatory certification mark for all processed fruit products, such as jams, squashes, pickles, canned fruits, and fruit beverages, ensuring they meet specific quality and hygiene standards. Option B, ISI (Indian Standards Institute) mark, is a certification mark for industrial products indicating compliance with Indian standards. Option C, Rugmark, is a certification mark used on carpets to indicate that they were not made with child labor. Option D, Agmark, is a certification mark for agricultural products (like spices, oils, pulses, etc.) signifying quality and purity, but FPO is specifically mandated for *processed fruit products*. Therefore, for fruit products, FPO is the mandatory mark.