Which two of the following organic compounds belong to thesame homologous series?
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 ,
  ,
 

To determine which two organic compounds belong to the same homologous series, we need to compare their structures and functional groups.

The given compounds are:

1. 
   
2. 
    
3. 
    
4. 
    

First, let's identify the functional groups present in each compound.

1. 
   : This compound has a single bond between carbon atoms and no functional groups.
2. 
    : This compound also has a single bond between carbon atoms and no functional groups.
3. 
    : This compound has a double bond between carbon atoms, indicating the presence of an alkene functional group.
4. 
    : This compound has a triple bond between carbon atoms, indicating the presence of an alkyne functional group.

Now, let's compare the functional groups of the compounds. Compounds 1 and 2 have the same functional group, which is no functional group. Therefore, compounds 1 and 2 belong to the same homologous series.

In summary, the two compounds that belong to the same homologous series are
 and
 .