I see the formula Al(OH)3.
Why are parentheses used in writing this formula?
The formula Na2O means we have two atoms of Na and one atom of O.
The formula Al(OH)3 means we have one atom of Al and three atoms of O and three atoms of H. Or, in other words, the subscript multiplies everyting INSIDE the parentheses.
Ba(NO3)2 means we have one Ba and two nitrate ions OR 2 Ns and 6 Os.