Determine the charge of the nucleus, the number of electrons and the mass of the atom if the nucleus contains 8 protons and 9 neutrons.

The number of electrons in an atom of any chemical element is equal to the ordinal number in the periodic table. Also, the number of electrons is equal to the number of protons. The nuclear charge is positive, and is numerically equal to the number of protons. The mass of an atom is equal to the sum of protons and neutrons.
So, 8 protons means that the ordinal number of the element in the table is 8. This is Oxygen O. The charge of the O nucleus is +8. The number of electrons = 8. The mass of the atom = 17. (8 protons + 9 neutrons).