According to Thomson model, an atom possesses a spherical shape in which the positive charge is accumulated at the centre.
False
Lets take a look at Thomson's model.
In 1898, J.J. Thomson proposed that an atom possesses a spherical shape (radius approximately 10−10m) in which the positive charge is uniformly distributed. Electrons are embedded into it more or less uniformly distributed. Electrons are embedded into it more or less uniformly to give the most stable electrostatic arrangement. This model of atom is known as plum pudding model or raisin pudding model or watermelon model. This model can be visualized as pudding or watermelon of positive charges with plums or seeds (electrons) embedded into it.
This model assumed that the mass of an atom is uniformly distributed over the atom.
⇒ The positive charge is uniformly distributed instead of being accumulated at centre in his model.