Question

isotopes are atoms of the same element that have the same number of __________ but different number of __________. therefore, isotopes of the same element have different masses.
protons, neutrons
protons, electrons
electrons, protons
neutrons, protons

Explanation:

Isotopes are defined as atoms of the same element. The atomic number (which is determined by the number of protons) defines an element. So, isotopes must have the same number of protons. The mass number of an atom is the sum of protons and neutrons. Since isotopes have different masses, they must have different numbers of neutrons. Electrons are not relevant here as they are involved in chemical bonding and do not contribute significantly to the mass (their mass is negligible compared to protons and neutrons).

Answer:

A. protons, neutrons