Give reasons for the following:
$(a)$ Isotopes of an element are chemically similar.
$(b)$ An atom is electrically neutral.
$(c)$ Noble gases show least reactivity.
$(d)$ Nucleus of an atom is heavy and positively charged.
$(e)$ Ions are more stable than atoms.

(N/A) Isotopes of an element have the same atomic number and electronic configuration. Since chemical properties are determined by electronic configuration,isotopes exhibit similar chemical behavior.
$(b)$ An atom contains an equal number of protons (positively charged) and electrons (negatively charged). The opposite charges cancel each other out,making the atom electrically neutral.
$(c)$ Noble gases have a complete outermost shell (stable octet or duplet configuration),which makes them chemically inert or least reactive.
$(d)$ The nucleus contains protons and neutrons. Protons are positively charged,and since both protons and neutrons have significant mass compared to electrons,the nucleus is heavy and positively charged.
$(e)$ Ions are more stable because they have achieved a complete valence shell (stable octet or duplet),similar to the configuration of noble gases.