Question

An ion ${\mathrm{M}}^{+2}$ contains 10 electrons. What is the atomic number of M?

Answer 1

Atomic number:

• It is defined as the number of protons present in an atom.
• It can also be defined as the number of electrons present in an atom in its neutral state.
• If an ion is represented as ${\mathrm{M}}^{+2}$ it means that the atom has lost its 2 electrons.
• So, the total number of electrons in an atom in its neutral state will be :
• $$\begin{gathered} =\mathrm{Electrons}\mathrm{of}{\mathrm{M}}^{+2}+2\mathrm{electrons} \\ =10+2 \\ =12\mathrm{electrons} \end{gathered}$$

Hence, the atomic number of the ion will be 12 because its atom will have 12 electrons in its neutral state.