Oh my god, you're totally right! Well spotted!Jase said:hmm.. well 2,3-dicholoro-4-methylpentane is an isomer of 1,2-dichlorohexane isn't it?.. both have C.6 H.12 Cl.2
You've moved a carbon to form a methyl group, and just moved the chlorines, but it's got the same molecular formula.
C is not an isomer of 1,2-dichlorohexane, it IS 1,2-dichlorohexane.
So the answer is A.