(a) The 4th member of the alcohol homologous series (n = 4) is Butan-1-ol.
Structural formula: CH₃–CH₂–CH₂–CH₂–OH
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(b) When ethanol is heated with alkaline KMnO₄, it gets oxidised to ethanoic acid.
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{alk. KMnO}_4/\Delta} \text{CH}_3\text{COOH}$$
Alkaline KMnO₄ acts as an oxidising agent.
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(c) When ethanol reacts with ethanoic acid in the presence of conc. H₂SO₄, esterification reaction takes place:
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \underset{\Delta}{\overset{\text{conc. H}_2\text{SO}_4}{\rightleftharpoons}} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
The product ethyl ethanoate is an ester with a sweet fruity smell.
Source: Carbon and its Compounds, Ethanol and its reactions
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