* Isotopes: Isotopes of the same element have the same number of protons but different numbers of neutrons.

* Neutrons: The difference in neutrons between isotopes determines their mass number.

Calculations:

* Isotope 1: 6 neutrons

* Isotope 2: 8 neutrons

This means the difference in mass number between the two isotopes is 2 (8 - 6 = 2).

Finding the Element:

* Since the number of protons defines the element, we need to find an element where the difference between its two most common isotopes is 2.

* Looking at the periodic table, we find that Carbon (C) has two common isotopes: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons).

Therefore, the element with 2 isotopes, one with 6 neutrons and the other with 8 neutrons, is Carbon (C).