(N/A) The ozonolysis of $o-$xylene ($1, 2-$dimethylbenzene) yields three products: methylglyoxal,$1, 2-$dimethylglyoxal,and glyoxal.
$o-$Xylene exists as a resonance hybrid of two Kekul\text{é} structures,labeled as $(I)$ and $(II)$.
Structure $(I)$ on ozonolysis gives $2$ moles of methylglyoxal $(CH_3COCHO)$ and $1$ mole of glyoxal $(CHOCHO)$.
Structure $(II)$ on ozonolysis gives $1$ mole of $1, 2-$dimethylglyoxal $(CH_3COCOCH_3)$ and $2$ moles of glyoxal $(CHOCHO)$.
Since the experimental mixture contains all three products (methylglyoxal,$1, 2-$dimethylglyoxal,and glyoxal),it confirms that $o-$xylene is a resonance hybrid of the two Kekul\text{é} structures $(I)$ and $(II)$.