The statement that is not true is: (b) The pellet is negatively charged.
Work Step by Step
Since the pellet is suspended, the electric force directed upward on the pellet is equal in magnitude to $mg$, the pellet's weight. The electric field points from positive charges to negative charges, so the electric field points upward. Since the electric force is directed upward, the pellet must have a positive charge. The statement that is not true is: (b) The pellet is negatively charged.