Isotopes of the same element must have the same number of - a protons + neutrons. b neutrons. c electrons. d protons.

D. Protons
Isotopes of the same element share the same amount of protons only. The number of neutrons can be determined depending on the molar mass of the element minus the number of protons. Example: Isotopes of Carbon are Carbon 12 and Carbon 14
Carbon 12 has a molar mass ( molecular weight) of 12 minus 6 protons it has will give you 6 neutrons.
Carbon 14 will have (14-6) = 8 neutrons.
The number of electrons will be the same in both elements as long as they remain as neutral elements

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