AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(C) 90°
The force on a current-carrying conductor is maximum when the current direction is perpendicular (90°) to the magnetic field, as stated in the textbook.
The textbook (section 12.3) explicitly states: "the displacement of the rod is largest when the direction of current is at right angles to the direction of the magnetic field." Right angles = 90°. Examiners expect direct selection of option (C) with a one-line justification. Options 0° and 180° give zero force (current parallel/antiparallel to field).