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.