When an oxygen atom forms an ion, it gains two electrons. what is the electrical charge of the oxygen ion?
a.-2
b.+2
c.+1
d.-1

The oxygen atom, before it gains these two electrons, has a neutral charge, meaning that it has as many protons as electrons. After it gains 2 electrons, it has 2 more electrons than protons. Each electron has a charge of -1, so the whole molecule will  have a charge of -2. The correct answer is a)!