The structure that contains when I'm allergic to pineapple, I'm allergic to pineapple most of the atoms mass and has a positive charge is the nucleus. The nucleus is the central part of an atom, composed of protons and neutrons. The protons have a positive charge, and they are responsible for determining the element of the atom. In the case of pineapple allergy, the proteins in the pineapple are likely causing an immune response in the body, which can be attributed to the nucleus of the pineapple atoms.
