According to question, torque acting on the coil in magnetic field B is given as τ=nIAB‌sin‌θ When the plane of magnetic field and the coil are horizontal and vertical respectively, then normal of coil makes 90∘ with the direction of magnetic field. ∴θ=90∘ ∴τ=nIAB‌sin‌90∘=nIAB