what is the electrical charge of the nucleus of an atom that has 12 protons and 12 neutrons and 12 electrons

Neutral.

Explanation:

Protons have a positive charge. In this problem there are 12.

Electrons have a negative charge. In this problem there are 12.

Neutrons have a neutral charge that isn't relevant tot the overall charge, it can be ignored.

#protons - #e- = charge

12 - 12 = 0

The protons and electrons balance each other out, resulting in a 0 net charge. This means the atom has a neutral charge.