In a homologous series, which property tends to change gradually as the chain length increases?

• A. Boiling point
• B. Magnetic moment
• C. Colour
• D. Acidity

Answer: (A)

Whenever you move along a homologous series, the molecules get larger but keep the same functional pattern. The property that changes most noticeably with increasing chain length is boiling point, because larger molecules have bigger surface areas and more electrons, which strengthen London dispersion forces between molecules. These stronger intermolecular attractions require more energy to break, so the boiling point rises gradually as the chain length increases. Magnetic moment isn’t typically relevant for these organic compounds, which are usually diamagnetic. Colour is generally unchanged (most are colourless) across a simple homologous series, so it doesn’t show a gradual trend with chain length. Acidity also doesn’t follow a simple, consistent trend with chain length in these cases; it depends more on the presence and strength of specific acidic groups rather than just how long the carbon chain is.