The values of electronegativity of atoms A and B are 1.20 and 4 respectively. The percentage ionic character of A-B bond is :

A formula for calculating ionic character is as follows:

$\% \mathrm{ionic} \mathrm{character}=16\left[{\mathrm{E}}_{\mathrm{A}}-{\mathrm{E}}_{\mathrm{B}}\right]+3.5{\left[{\mathrm{E}}_{\mathrm{A}}-{\mathrm{E}}_{\mathrm{B}}\right]}^2$

$\% \mathrm{ionic} \mathrm{character}=16[4-1.2]+3.5[4-1.2{]}^2$

$\% \mathrm{ionic} \mathrm{character}=72.24$.

Hence, the option B is correct.