The correct option is A positive
In the gold foil experiment, Rutherford bombarded a thin layer of gold foil with alpha particles. He observed that:
(i) Most of the alpha particles went through the foil undeviated. This indicated that most of the space inside the atom is empty.
(ii) Few alpha particles were deflected from their path indicating the presence of positive charge at the centre.
(iii) Very few particles were deflected by 1800. This indicated that the positive charge and the mass is concentrated in a small volume at the center of the atom.