(i) Carbon cannot form C⁴⁺ or C⁴⁻:
To form C⁴⁺, carbon would need to remove 4 electrons, requiring a very large amount of energy, which is not energetically feasible. To form C⁴⁻, it would need to gain 4 electrons; placing 4 extra electrons on a small carbon nucleus would be very difficult as the nucleus cannot hold so many electrons with stability. Therefore, carbon shares electrons and forms covalent bonds instead.
(ii) Homologous Series:
A homologous series is a group of organic compounds having the same general formula and similar chemical properties, differing from each other by a –CH₂– unit.
C₄H₁₀ has more carbon atoms and hence greater molecular mass than C₃H₈ or C₂H₆. Greater molecular mass means stronger intermolecular forces (van der Waals forces), so more energy is needed to overcome them, resulting in higher melting and boiling points.
(iii) Oxidation of Ethanol:
When ethanol is heated with acidified potassium dichromate, it gets oxidised to ethanoic acid (acetic acid). The orange colour of potassium dichromate changes to green.
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{acidified K}_2\text{Cr}_2\text{O}_7} \text{CH}_3\text{COOH}$$
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