If two atoms of an element are isotopes, then they have a different A. Atomic symbol
B. Number of protons
C. Number if neutrons
D. Number of electrons
E. Atomic number

Number if neutrons

Explanation:

same number of protons, but some may have different numbers of neutrons. For example, all carbon atoms have six protons, and most have six neutrons as well. But some carbon atoms have seven or eight neutrons instead of the usual six. Atoms of the same element that differ in their numbers of neutrons are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same physical and chemical properties. That's because they have the same numbers of protons and electrons.

a electronegativity decreases beacuse the size of nucleus is bigger.