Define orbital? What are the $\mathrm{n} \& \mathrm{l}$ values for$3{\mathrm{p}}_{\mathrm{x}}$ and$4{\mathrm{d}}_{{\mathrm{x}}^2-{\mathrm{y}}^2}$ electron? 

An atom of an element contains $29$ electrons and $35$ neutrons. Deduce

(i) The number of protons and
(ii) The electronic configuration of the element.

 Indicate the number of unpaired electrons in: (a) $\mathrm{P}$, (b) $\mathrm{Si}$, (c) $\mathrm{Cr}$, (d) $\mathrm{Fe}$, (e) and $\mathrm{Kr}$.

Sodium and chlorine are in the same period of the Periodic Table.

Write the electronic configuration of ${\mathrm{N}\mathrm{a}}^{+}$ and ${\mathrm{C}\mathrm{l}}^{-}$ ions.
(Atomic number: $\mathrm{Na}=11$and $\mathrm{Cl}=17$)