Question

What is the chemical formula of aluminium oxide?

• A. $AlO$
• B. ${Al}_3{O}_2$
• C. ${Al}_2{O}_3$
• D. $Al{O}_2$

Answer 1

The correct option is C ${Al}_2{O}_3$

$\bullet$ The combining elements of aluminium oxide are aluminium and oxygen.

$\bullet$ The chemical formula of a compound is obtained by a short-cut method of cross-multiplication of their valencies.
$$\begin{array}{ccc}& \text{Aluminium}& \text{Oxygen}\\ \text{Symbol}& \text{Al}& \text{O}\\ \text{Valency}& \text{3}& \text{2}\end{array}$$
$\bullet$ After cross-multiplication of the valencies, we get the formula of the compound as ${\text{Al}}_2{\text{O}}_3$.