Which of the following does not belong to the same homologous series?

Name the functional group present in the following compounds:
$(i)$ $CH_{3}-CH_{2}-CH_{2}-COOH$
$(ii)$ $CH_{3}-CO-CH_{2}-CH_{3}$

What is the percentage of sulfur used in vulcanized rubber for battery casings (in $\%$)?

Describe a chemical test to distinguish between ethanol and ethanoic acid.

On dropping a small piece of sodium in a test tube containing carbon compound $X$ with molecular formula $C_{2}H_{6}O$,a brisk effervescence is observed and a gas $Y$ is produced. On bringing a burning splinter at the mouth of the test tube,the gas evolved burns with a pop sound. Identify $X$ and $Y$. Also,write the chemical equation for the reaction. Write the name and structure of the product formed when you heat $X$ with excess concentrated sulphuric acid.

What is hydrogenation? What is its industrial application?