Observe the following reaction:

${\mathrm{BF}}_3+{\mathrm{NH}}_3⟶\left[{\mathrm{F}}_3\mathrm{B}⟵{\mathrm{NH}}_3\right]$

Choose the correct statement regarding product :

To achieve a stable electronic state, an element must share electrons with other atoms of the same or different elements.

In the reactant part, the boron shares 3 electrons with the fluorine. While in the product 4 electrons with the fluorine. 

Hence, Covalency of B is changed from 3 to 4.