Answer 1

The general formula for the homologous series of functional group −Cl is C_nH_2n+1Cl.

The two consecutive members of this series are:

a. CH₃Cl (Chloromethane)

b. CH₃CH₂Cl (Chloroethane)

where n is 1 and 2 respectively
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The molecular formula for both of them are CH₃Cl and C₂H₅Cl.