Question

observe the picture above.
what changes between isotopes?
atomic number
number of protons
number of neutrons
number of electrons

Explanation:

Isotopes are atoms of the same element. The atomic number (which is equal to the number of protons) defines an element, so isotopes have the same atomic number and number of protons. In a neutral atom, the number of electrons equals the number of protons, so the number of electrons is also the same for isotopes. However, isotopes differ in the number of neutrons.

Answer:

Number of neutrons