The overall charge of the nucleus portion of an atom is positive. The nucleus contains positively charged particles called protons, which have a charge of +1 elementary charge. The number of protons in the nucleus determines the atomic number of the atom, which defines its identity as an element.
However, the nucleus also contains particles called neutrons, which have no charge (charge of 0). Neutrons contribute to the mass of the atom but not to its overall charge.
The positive charge of the protons in the nucleus is balanced by the negative charge of electrons in the electron cloud surrounding the nucleus. The number of electrons is equal to the number of protons in a neutral atom, resulting in an overall neutral charge for the atom as a whole.