How can two atoms of the same chemical element be different?
a.
they may be different allotropes of the element. each allotrope of the same element has a different number of electrons.
b.
they may be different isotopes of the element. each isotope of the same element has a different number of electrons.
c.
they may be different allotropes of the element. each allotrope of the same element has a different number of neutrons.
d.
they may be different isotopes of the element. each isotope of the same element has a different number of neutrons.