If the electronegativity difference between two atoms A and B is 2.0, the percentage of covalent character in the molecule is : 

According to Hannay and Smith equation, 
$\mathrm{\%}\text{ ionic character }=16\left({\mathrm{X}}_{\mathrm{A}}-{\mathrm{X}}_{\mathrm{B}}\right)+3.5{\left({\mathrm{X}}_{\mathrm{A}}-{\mathrm{X}}_{\mathrm{B}}\right)}^2$
Where, X_A and X_B are the electronegativities of the atoms A and B respectively.
$$\begin{gathered} \therefore \mathrm{\%}\text{ ionic character }=16\left(2\right)+3.5(2{)}^2=32+14=46\mathrm{\%} \\ \mathrm{\%}\text{ covalent character }=100-46=54\mathrm{\%} \end{gathered}$$