(i) Carbon has 4 valence electrons. To form C⁴⁺, it would need to lose 4 electrons, requiring a very large amount of energy. To form C⁴⁻, it would gain 4 electrons, but it would be difficult to accommodate 4 extra electrons on the small carbon nucleus — both are energetically unfavourable. Instead, carbon shares its 4 valence electrons with other atoms, forming 4 covalent bonds, which is much more stable.
(ii) A homologous series is a series of carbon compounds having the same functional group and similar chemical properties, where each successive member differs by –CH₂– (molecular mass difference of 14 u).
Two consecutive members of the aldehyde homologous series:
(iii) Structure of Cyclohexane (C₆H₁₂):
$$\begin{array}{c}
\text{Each carbon in the ring is bonded to 2 H atoms}\\[4pt]
\underset{H_2}{\overset{H_2}{C}}\!-\!\underset{H_2}{\overset{H_2}{C}}\text{ (hexagonal ring)}
\end{array}$$
Structural representation:
Each carbon carries 2 hydrogen atoms in a six-membered ring:
```
CH₂—CH₂
/ \
CH₂ CH₂
\ /
CH₂—CH₂
```
Source: Chapter 4, Sections 4.2.2 and 4.2.5
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