Which group is always taken as a substituent in the `IUPAC` system of nomenclauture ?

Which group is always taken as a substituent in the IUPAC system of nomenclature ?

0! is always taken as

Which group is always used as substitudent in the IUPAC nomeclature ?

Which group is always taken as substituent in IUPAC nomenclature of compound ?

The correct decreasing order of priority for the functional groups of organic compounds in the IUPAC system of nomenclature is