Q.Name the alkane from which methyl benzene is obtained by reforming.

Step 1. Recall the reforming/aromatization reaction. Section 15.1.5 describes reforming as converting a straight-chain alkane of 6-10 carbons into benzene or a homologue, with n-hexane (exactly 6 carbons) giving plain benzene plus 4 H2.

Step 2. Work out the carbon count needed for toluene. Methylbenzene (toluene) is a benzene ring (6 ring carbons) carrying one extra methyl substituent -- 7 carbons in total. Since reforming cyclises the first 6 carbons of a straight chain into the ring and leaves any carbons beyond that as a substituent on the ring, a 7-carbon straight-chain alkane is exactly what is needed.

Step 3. Name the alkane. The straight-chain C7H16 alkane is n-heptane; reforming it (dehydrogenation + cyclisation, same V2O5/Cr2O3-type catalyst, ~773 K, 10-20 atm as for hexane) gives methylbenzene (toluene) plus hydrogen gas.

Counting the carbons needed for a benzene ring (6) plus one methyl substituent (1) to find the required starting chain length, then naming that straight-chain alkane

• Answering 'n-hexane', forgetting that hexane's reforming gives PLAIN benzene (no substituent), not toluene, since it has exactly 6 carbons with none left over for a substituent.
• Not recognising that reforming/aromatization always uses the alkane's own carbons for both the ring AND any substituent -- it never adds an external methyl group from elsewhere.