The correct answer is: A. Along neutral axis.
The armature coil is short circuited by brushes when it lies along the neutral axis. This is because the brushes are located at the ends of the commutator, which is a cylindrical conducting ring that is divided into segments. When the armature coil is aligned with the neutral axis, the brushes are in contact with two adjacent segments of the commutator, and current flows through the coil without interruption.
Option B is incorrect because the field axis is perpendicular to the neutral axis. When the armature coil is aligned with the field axis, the brushes are not in contact with any segments of the commutator, and current cannot flow through the coil.
Option C is incorrect because the armature coil can only be short circuited by brushes when it lies along the neutral axis. If the armature coil is in any other position, the brushes will not be in contact with any segments of the commutator, and current cannot flow through the coil.
Option D is incorrect because the armature coil is short circuited by brushes when it lies along the neutral axis.