Question

Atoms of the same element are alike because they must have the same number of:

electrons

protons

neutrons

both protons and electrons

Answer 1

Protons. If a element does that have the same number of protons as the atomic number, it's not the same element..

Answer 2

Atoms of same element must have equal number of protons in their nuclei i.e. have same atomic number while number of neutrons may vary i.e. the case of isotopes.
Atom as a whole is neutral and the number of positively charged protons in the nucleus is always equal to the number of negatively charged electrons revolving around the nucleus.
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