Correct option is C
The most likely cause of heavy sparking in the brushes of a DC generator is Change in position of MNA.
ExplanationWhen the brushes are not properly positioned relative to the Magnetic Neutral Axis (MNA), the current flow in the armature conductors might not be smoothly reversed, leading to sparking. The MNA is the point where the induced emf in the armature conductors is zero, and the brushes should be placed on this axis to ensure smooth commutation.
