According to Thomson Model of an atom(1898), an atom takes the spherical shape and the positive charge is evenly distributed all over the sphere and also the mass is assumed to be uniformly distributed all over the atom.

These positive charge and mass get neutralised by electrons which are fixed in the sphere in such a manner that it gives rise to most stable electrostatic orientations and therefore causes overall neutrality of atoms. (the plum pudding or watermelon like structure where the positive charge is the plum and the electrons are embedded in it just like seeds )

Hence other 3 options,(ii)Spectra of a hydrogen atom. (iii) Position of electrons, protons and neutrons in an atom. (iv) Stability of atom is incorrect because J.J Thomson’s atomic model fails to give an explanation for them.