General formula defines alkane homologous series Steps:

• Homologous series are organic compounds with the same functional group, general formula, and properties that vary gradually.
• Alkanes are saturated hydrocarbons containing only C-C and C-H single bonds.
• Each successive member differs by a -CH2- unit, leading to the formula CnH2n+2.
• Examples confirm: methane (n=1, CH4), ethane (n=2, C2H6), butane (n=4, C4H10).

Why B is correct:

• CnH2n+2 is the defining general formula for the alkane homologous series, allowing prediction of molecular structure.

Why the others are wrong:

• A: Alkanes are saturated; unsaturated hydrocarbons contain multiple bonds like in alkenes (CnH2n).
• C: Boiling points increase with carbon atoms due to larger size and stronger van der Waals forces.
• D: Liquid alkanes do become more viscous with increasing mass, but this is a physical trend, not the core definition of the series.

Final answer: B