An uncharged atom of mercury has an atomic number of 80 and an atomic mass of 200. this atom has protons, neutrons, and electrons

             This atom has 80 protons, 120 neutrons and 80 electrons.

Number of Protons:

                               As the number of protons present in the nucleus are equal to the atomic number therefore. As given, the atomic number is 80 therefore, Hg contains 80 protons respectively.

Number of Electrons:

                                 As given in statement, Hg is not carrying any type of charge. It means this atom is neutral in nature. Which means, it is carrying the same number of electrons as the number of protons in order to give a neutral atom. Therefore, it contains 80 electrons.

Number of Neutrons:

                                 Number of neutrons can be calculated using following formula,

                  No. of Neutrons  =  Atomic Mass - Number of Protons

As,

                                    Atomic Mass  =  200

So,

                                    No. of Neutrons  =  200 - 80

                                    No. of Neutrons  =  120