${\mathrm{AB}}_3$ is an interhalogen T-shaped molecule. The number of lone pairs of electrons on A is ______________.(Integer answer)

T-shaped molecule it involves ${\mathrm{sp}}^3\mathrm{d}$ hybridization that means it has 3 sigma bond and 2 lone pairs of electron on central atom.

Hence, correct option is : 2 lone pairs.