If element x has 78 protons, how many electrons does it have?

In its unionized state it would have 78 electrons as well. The platinum atom has

117 neutrons

78 electrons

78 protons.

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.