Which of the following has maximum hydrogen/carbon ratio (by weight)?

Hydrogen to carbon (H/C) ratio is higher for lighter hydrocarbon fractions and decreases as the molecular weight increases.

Naphtha is a lighter petroleum fraction composed of smaller hydrocarbon molecules, so it has a higher hydrogen content relative to carbon.

Gasoline is slightly heavier than naphtha and therefore has a lower H/C ratio compared to naphtha.

Diesel contains longer hydrocarbon chains, resulting in a further reduced hydrogen to carbon ratio.

Fuel oil is the heaviest among the options with large, complex molecules and thus has the lowest H/C ratio.

Hence, naphtha has the maximum hydrogen/carbon ratio among the given options.