<h3><u>Answer;</u></h3>
3 Mg, 6 O, and 6 H
<h3><u>Explanation;</u></h3>
<em><u>Mg(OH)2 is a compound made up of 1 atom of magnesium, 2 atoms of oxygen, 2 atoms of hydrogen</u></em>.
<em><u>3Mg(OH)2, means 3 formula units of Mg(OH)2; the number of atoms present will be; 3 magnesium atoms, 6 oxygen atoms and 6 hydrogen atoms.</u></em>
That is; 3 × 1 Mg atom = 3 magnesium atom
3 × 2 Oxygen atoms = 6 oxygen atoms
3 × 2 Hydrogen atoms = 6 hydrogen atoms