In which of the following molecule all the carbon-carbon bonds are not equal.

[Step 1]:In option 1) Ethane  H3C−CH3 contain one C-C bond.[Step 2]:In option 2) Propane H3C−CH2−CH3 all three carbons are SP3 and are equal.[Step 3]:In option 3) Propdiene H2C=C=CH2 all carbons are SP2 and are equal.[Step 4]:In option 4) Propene H3C−CH=CH2 one carbon is SP3 and other two carbons are  SP2. Therefore all carbons are not equal.