Question

1. isotopes of the same element differ in the number of: orbitals neutrons electrons protons

Explanation:

Isotopes of an element have the same number of protons (which defines the element) and electrons (in a neutral state). They differ in the number of neutrons, which affects their atomic mass. Orbitals are related to electron - distribution and not what differentiates isotopes.

Answer:

B. Neutrons