Question

what must differ between the atom of two different elements?
o protons in the atom
o electrons in the atom
o neutrons in the atom
o protons and neutrons in the nucleus

Explanation:

The atomic number, which is determined by the number of protons in an atom's nucleus, defines the element. Different elements have different atomic numbers, so the number of protons in the atom must differ between atoms of two different elements. Electrons can vary in ions and isotopes can have different neutron - numbers for the same element.

Answer:

protons in the atom