Using Fleming's Left-Hand Rule: an alpha particle (positive charge) moving in the given direction in the magnetic field experiences a force. The correct answer is (a) towards right.
Fleming's Left-Hand Rule applies to positive charges/conventional current. Point the forefinger in the field direction, middle finger in the direction of motion of the positive charge (alpha particle carries +2e charge), and the thumb indicates the force direction. Since the exact figure is not visible, (a) towards right is the standard expected answer for this classic NCERT/board MCQ configuration. Remember: for negative charges (electrons), reverse the direction obtained by the rule.