answer 12 question....
Answers
1. Isotopes of an elements are chemically similar because they have the same number of electrons as an atom of that element.
2. An atom is electrically neutral because they have equal number of protons and electrons.
3. The noble gases show least reactivity because the have a filled valence shell of electrons.
4. Nucleus only consists of proton and neutron. Proton has positive charge whereas neutron has no charge that means the net charge on nucleus is positive. Nucleus is heavy because it carry proton and neutron.
5. Atoms are generally stable. But if there is any loss in their stability, they gain or loss the electron to acquire stability and become ions. That means both atom and ions are stable, while atoms are stable by default whereas ions become stable by gaining or losing the electron.