The answer is Cs and F. S and O are both non-metals and if I am not mistaken they are both on the right side of the periodic table. S and O exhibit a covalent bond, the other pairs do too except for the first pair of atoms. Therefore, the answer is A. Cs and F.
<span>You need to consider the valences of the two elements. Potassium is +1; nitrogen is -3. To balance the molecule, you need 3 potassium to one nitrogen, or K3N</span>
