According to the Bohr Bury rule, the maximum number of electrons in a particular orbit is given by the formula $2{\mathrm{n}}^{\mathrm{a}}$. Here, the value of a will be . $(2, 4, 6)$

The schematic atomic structure of four elements is given below. Observe and choose the right statement.

An isoelectronic species are

$$\begin{gathered} \mathrm{a}\left){\mathrm{Na}}^{+} \\ \mathrm{b}\right){\mathrm{Al}}^{3+} \\ \mathrm{c}\left){\mathrm{Mg}}^{2+} \\ \mathrm{d}\right){\mathrm{Ca}}^{2+} \end{gathered}$$

Nitrogen (atomic number $7$) and phosphorus (atomic number $15$) belong to group $15$  of the Periodic Table. Write the electronic configuration of these two elements. Which one of these will be more electronegative? Why? 

What do you understand by the term electronic configuration? State Bohr-Bury's scheme of electronic configuration.