Question

pineapple jam can be kept for a longer period than pieces of pineapple ?why

Answer 1

In pineapple jam , preservatives are added to prevent spoilage/to preserve for long period of time. Whereas , in pineapple  no preservatives are added.
Therefore, Pineapple jam can be kept for a longer period than pieces of pineapple 

Answer 2

In pineapple jam, chemicals are added to limit deterioration which helps to preserve the jam for the long period of time. However, in fresh pineapple pieces, as they are natural so no chemicals are added.

Therefore, Pineapple jam can be retained for a longer period of time than slices of pineapple