Explain how the isotopes of an element differ. (1 point) they each have a different number of electrons in their outermost energy level. they each have a different number of protons in their nuclei. they each have a different number of neutrons in their nuclei. they each have a different charge.,

They each have a different number of neutrons in their nuclei.

Every atom consists of 3 basic particles, protons, neutrons, and electrons. The actual element is determined by the number of protons, and for a neutral atom, each proton has a corresponding electron. The neutrons which have no charge are in the nucleus and may have a different count for different isotopes of the same element. With that in mind, let's look at the options:

They each have a different number of electrons in their outermost energy level.
* This is constant for each element if the atom has a neutral charge. It can be changed electrically, but that doesn't affect what isotope it is, so this is a bad choice.

They each have a different number of protons in their nuclei.
* If the number or protons change, then you have a different element. So this is a bad choice.
They each have a different number of neutrons in their nuclei.
* This is the correct choice.

They each have a different charge.
* The electrical charge doesn't affect what the isotope is, so this is a bad choice.

The answer is observations and interpreting.