from your knowledge about the distribution of electrons in their shells and from the atomic number (in parentheses), indicate the most likely charge on the ion when this atom forms an ion. (remember the 2-8-18 shell distribution.)

oxygen (8)

+1
+2
-2
-1

The correct option is -2.

Explanation:

Oxygen atom will have two electrons in its first shell and six electrons in its outermost, valence shell. To become stable, an oxygen atom will need to gain two electrons so that it has 8 electrons in its outermost, valence shell. When oxygen will gain two electrons from another atom, it will get a charge of -2. This is because it has acquired two more negative charged electrons. Hence, the correct option is -2.