Milk of magnesia has the chemical formula mg(oh)2. what is the mass of 3.2 moles of milk of magnesia? the molar mass of magnesium is 24.3 grams per mole. the molar mass of hydrogen is 1.0 grams per mole. the molar mass of oxygen is 16.0 grams per mole

The answer is 186.56 g.

The molar mass (Mr) of Mg(OH)₂ is the sum of atomic masses (Ar) of the elements.
Ar(Mg) = 24.3 g/mol
Ar(H) = 1
Ar(O) = 16

Mr(Mg(OH)₂) = Ar(Mg) + 2Ar(O) + 2Ar(H) = 24.3 + 2*1 + 2*16 = 24.3 + 2 + 32 =  58.3 g/mol

Now, make a proportion. If 58.3 g are in 1 mol, how much will be in 3.2 mol:
58.3 g : 1 mol = x : 3.2 mol
x = 58.3 g · 3.2 mol ÷ 1 mol = 186.56 g

They are all full and don't need any more electrons in there outer shell.