How many products are obtained by the substitution of two hydrogen atoms in a benzene ring? Provide examples.

(N/A) When two hydrogen atoms are substituted in a benzene ring,the number of possible isomers is $3$.
These are $1,2-$disubstituted (ortho),$1,3-$disubstituted (meta),and $1,4-$disubstituted (para).
Examples include:
$1,2-$Dimethylbenzene ($o-$xylene)
$1,3-$Dimethylbenzene ($m-$xylene)
$1,4-$Dimethylbenzene ($p-$xylene)
$o-$Nitrotoluene
$m-$Nitrotoluene
$p-$Nitrotoluene