How the positively charged particles are shielded fromthe negatively charged particles without neutralised ?

Dear student,

Electrostatic shiedling is due to the induction of charges on the surface of conductor such that the net electric field inside the whole conductor(even inside the cavity) is zero. Hence due to charge distribution present outside(due to which the external electric field is present) and the induced charges on the outer surface of the conductor, the net force acting on any charge inside(positive or negative) is zero.

Also, you could be more specific about the case you have the query about. All the best!