CnH2n+2 belongs to the family of alkanes which has only single bond between them they only consists of Sigma bonds. ETHANE (C2H6)
CnH2n it belongs to the family of alkenes which has at least one double bond between them or in ring form they also have Sigma bonds but also contain a pi bond for example in the structure of ethene (C2H4)we have a Pi bond.
CnH2n−2 it belong to the family of alkyne which has at least one triple bond where in which can be 2 pi bonds. For example ethyne (C2H2)
CnH2n+1 it belong to the family of alkyl group.
CH2 it belong to the family of methylene group.