Give the molecular and structural formulae of the first four members of the homologous series of alkanes.

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Solution

The homologous series of alkane differs from only one Carbon ( $C$ ) and 2 Hydrogen ( $H$ ) atoms i.e. by addition of $C H_{2}$ group in successive alkane compounds.
Thus, they have a general molecular formula of $C_{n} H_{2 n + 2}$ . Here n is the number of Carbon atoms ( $C$ ) present in the compound.
Therefore, the first four members of the homologous series of alkanes are as follows.
For n = 1, $C H_{4}$ (Methane)
For n = 2, $C H_{3} - C H_{3}$ (Ethane)
For n = 3, $C H_{3} - C H_{2} - C H_{3}$ (Propane)
For n = 4, $C H_{3} - C H_{2} - C H_{2} - C H_{3}$ (Butane)

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