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

Note the atom of the Oxygen is electrically neutral, meaning it has equal numbers of electrons and protons.

So if it gains 2 electrons, it would have excess of 2 electrons, hence its charge would be -2.

Option B.