$A$ box contains some identical red-coloured balls,labelled as $A$,each weighing $2 \ g$. Another box contains identical blue-coloured balls,labelled as $B$,each weighing $5 \ g$. Consider the combinations $AB, AB_2, A_2B$ and $A_2B_3$ and show that the law of multiple proportions is applicable.

(N/A) To verify the law of multiple proportions,we calculate the mass of $B$ that combines with a fixed mass of $A$ $(4 \ g)$:

Combination	Mass of $B$ combined with $4 \ g$ of $A$
$AB$	$10 \ g$
$AB_2$	$20 \ g$
$A_2B$	$5 \ g$
$A_2B_3$	$15 \ g$

The masses of $B$ that combine with a fixed mass of $4 \ g$ of $A$ are $10 \ g, 20 \ g, 5 \ g$ and $15 \ g$.
The ratio of these masses is $10:20:5:15$,which simplifies to $2:4:1:3$.
Since this is a simple whole-number ratio,the law of multiple proportions is applicable.