Number of Mg (OH) 2 formula units in 7.40 moles of Mg (OH) 2.

The answer is 4.45 * 10²⁴ units.

To calculate this, we will use Avogadro's number which is the number of units (atoms, molecules) in 1 mole of substance:

6.02 * 10²³ units per 1 mole

So, we need a proportion:

If 6.02 * 10²³ units are in 1 mole, how many units will be in 7.40 moles:

6.02 * 10²³ units : 1 mole = x : 7.40 moles

After crossing the products:

1 mole * x = 7.40 moles * 6.02 * 10²³ units

x = 7.40 * 6.02 * 10²³ units

x = 44.5 * 10²³ units = 4.45 * 10²⁴ unit