Here's why:

* Fe is the chemical symbol for iron.

* (III) indicates the iron ion has a +3 charge.

* OH is the hydroxide ion, which has a -1 charge.

* To balance the charges, we need three hydroxide ions (3 x -1 = -3) to neutralize the +3 charge of the iron ion.

Therefore, the formula for iron(III) hydroxide is Fe(OH)₃.