Question

write the molecular farmula of the 2nd and 3rd member of the homologus series whose first member is methane

Answer 1

If first member is ethane than 2nd &3rd members will be propane and butane which have molecular fomula C3H8 & C4H10

Answer 2

Hi !

Homologous series are those series , which have same general formula.

General formula for alkanes is $C _{n} H _{2n + 2}$

Here "n" denotes no: of carbon atoms.

First member of the homologous series of alkanes is Methane(CH₄)

Second and third member are ethane and propane.

Ethane ( n = 2)

$C _{2} H _{2*2 + 2}$ = C₂H₆

Ethane -> C₂H₆
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Propane  ( n = 3)


$C _{3} H _{2*3 + 2}$ = C₃H₈

Propane -> C₃H₈