Question

What is the chemical formula for aluminium oxide?

• A. ${Al}_2{O}_3$
• B. ${Al}_3{O}_2$
• C. $Al{O}_2$
• D. ${Al}_{2}O$

Answer 1

The correct option is A

${Al}_2{O}_3$

For Aluminium oxide, we write the symbol of cation $A{l}^{3+}$ first followed by the symbol of anion $O_2^{-}$ Then their charges are criss-crossed to get the formula.

Symbol: Al O

Valency: 3 2

Cross multiply both the valency

Or

The aluminum ion has a +3 charge, and the oxygen ion has a -2 charge. In order to balance, you need the same number of elements on each side of the equation. We need 2 Al on the left side and 3 O on the left side. But Oxygen is diatomic in its natural state, it occurs as a molecule consisting of two atoms. So here's what you do: Put 2 in front of Al and put $\frac{3}{2}$ in front of $O_2$.
2$Al$(s) + $\frac{3}{2}$ $O_2$ (g) = ${Al}_2{O}_3$ (s)

Therefore, ${Al}_2{O}_3$ is the chemical formula for aluminium oxide