Is it possible for the atom of an element to have one electron,one proton,and no neutron? If so,name the element.

$(a)$ An ion $M^{2+}$ contains $10$ electrons and $12$ neutrons. What is the atomic number and mass number of the element $M$?
$(b)$ Is it possible in an atom to have $12$ protons and $13$ electrons? Explain.
$(c)$ Why is helium gas inert?

The ion of an element has $3$ positive charges. The mass number of the atom is $27$ and the number of neutrons is $14$. What is the number of electrons in the ion?

Explain with examples $(i)$ Isotopes and $(ii)$ Isobars. Give any two uses of isotopes.

Isotopes of an element have

Give a reason to explain why
$(a)$ isotopes of an element show identical chemical properties?
$(b)$ the atomic masses of elements are in fractions?
$(c)$ atoms combine with other atoms?