C-36
To determine the nucleon number of an atom, we need to add the number of protons and neutrons together.
In this case, you mentioned that the atom is a divalent cation, which means it has a charge of +2. Since the charge is positive, it indicates that the atom has lost two electrons.
Given that the atom has 18 electrons, we subtract 2 from the total number of electrons to determine the number of protons. Thus, the number of protons would be 18 - 2 = 16.
The nucleon number (also known as the mass number) is the sum of protons and neutrons. So, adding the 16 protons to the given 20 neutrons, we get:
16 protons + 20 neutrons = 36 nucleons.
Therefore, the nucleon number of the atom will be 36.