By what mass do successive members of a homologous series differ as one -CH2- unit is added?

1. Moving to the next member adds one methylene (-CH2-) unit. 2. A -CH2- unit has one carbon (12 u) and two hydrogens (2 x 1 = 2 u). 3. Adding gives 12 + 2 = 14 u increase per step. 4. Rule out D: 12 u counts only the carbon and ignores the two hydrogens. 5. Rule out B: 16 u wrongly counts an extra hydrogen (a CH3 difference). 6. Rule out C: 28 u is two -CH2- units, the gap between alternate members. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 9 "Carbon Compounds", p.129_