Write the chemical formula of Aluminium hydroxide in a step-by-step manner.

Step 1 — Write each symbol with its valency

$\text{Al}^{3+} \phantom{\nearrow} \text{OH}^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{3}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{OH}} \Rightarrow \underset{\phantom{1}{1}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{OH}} \\[0.5em]$

Step 3 — Write the interchanged number & hence the formula

Therefore, we get

Formula of Aluminium hydroxide : $\bold{Al(OH)_3}$