Two atoms of the same element must have the same number of two atoms of the same element must have the same number of electrons protons neutrons plus protons neutrons

Option (b) is the correct answer.

Explanation:

When two atoms of the same element has different number of neutrons but same number of protons then it is known as an isotope.

For example, isotopes of carbon are and .

Also, when two atoms of the same element have same number of protons then their chemical properties remain the same.

Therefore, we can conclude that two atoms of the same element must have the same number of protons.