If the atomic number of an element X is 13.The number of electrons in its ion x3+ will be 10. This is because x3+ is a positively charged cation. An atom loses electrons from its valence shell and becomes positively charged ion called cation. Here, Atom X loses 3 electrons and acquires 3+ charge. therefore the number of electrons lost will be 3. and the number of electrons in its ion x3+ will be 10.