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The molecule appears to be ethyl benzene. The bonds should have sp2 hybrid orbitals in them. The molecule is least stable with the double covalent bond between the CH3 and CH2CH3 group.
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Nov 12th, 2015
The very bottom figure should be the most stable. because we want the sp2 hybrid orbitals for all 6 carbon atoms in the ring. each carbon atom in the ring is most stable when each have 3 bonded groups.