An ion has a charge of 2 - and 18 electrons.

A) From which atom does this ion form?

B) How do you know?

The answer to your question is:

Explanation:

Data

Ion charge of 2 - and 18 electrons

Process

a) From which atom does this ion form?

If an Ion has a negative charge, it means that it has more electrons than the neutral atom. So, it the ion has 18 electrons, it means the neutral atom has 16 electrons.

In the periodic table we find that the atom with 16 electrons is Sulfur.

B) How do you know?

I have explained it.

An ion with a negative charge means that it gained the number of negative charges compare with the neutral atom.