Dear Student,
Answer to your question is given below:
(a) If the rod is made of a good insulator, charges from the metal ball does not flow to the rod since insulator is a non-conductor of electric charge.
(b) If the rod is made of a poor insulator, charges from the metal ball flows to the rod but in very little amount since a poor insulator conducts electric charges but in very small amount.
(c) If the rod is made of a good conductor, charges from the metal ball flows easily to the rod since a conductor can easily transfer electric charges.
Regards,