Concept:C3H6Cl2 is a dichloro derivative of propane, so the chlorine atoms can occupy different positions on the 3-carbon chain.
Explanation:The carbon skeleton is only propane because a 3-carbon chain cannot form any other skeleton.
Place the two chlorine atoms in all possible arrangements:
1. 1,1-dichloropropane: both Cl atoms on the first carbon.
2. 2,2-dichloropropane: both Cl atoms on the middle carbon.
3. 1,2-dichloropropane: one Cl on the first carbon and one Cl on the second carbon.
4. 1,3-dichloropropane: one Cl on each terminal carbon.
Thus, there are exactly 4 structural isomers.
Answer:4 isomers, i.e. Option C.