Question

The formula of aluminium oxide is ${\text{Al}}_2{\text{O}}_3$. If aluminium forms its chloride, what will be the formula of that compound?

• A. $\text{AlCl}$
• B. ${\text{AlCl}}_2$
• C. ${\text{Al}}_3\text{Cl}$
• D. ${\text{AlCl}}_3$

Answer 1

The correct option is D ${\text{AlCl}}_3$

In ${\text{Al}}_2{\text{O}}_3$, the valency of aluminium is $3$ and oxygen is $2$.
The valency of chlorine is $1$.
So, for a chloride of aluminium: Symbol Valency

$\text{Al}$	$\text{Cl}$
$3$	$1$

On interchanging the valencies of each element and​ writing them down as subscripts, we get the formula - ${\text{AlCl}}_3$.