Fluoride content is least –
Amongst the given options isoflurane produces minimum fluoride.

Methoxyflurane → 50 m
Sevoflurane → 30 - 50 m
Enflurane → 20 - 25 in
Isoflurane → 4 - 8 m
Halothane → Only in anaerobic conditions
Desflurane → Zero
Methoxyflurane
Enflurane
Isoflurane
Sevoflurane