1. This sounds like the condition for resonance. When you draw the dot structure of SO2, for example, there are several structures, two of which have octets on all the atoms and with a double bond to one oxygen or to the other:
O=S–O 
O–S=O
Imagine blending these two structures into one, which is what the actual SO2 molecule is (making the S–O bonds equivalent). In the molecular orbital picture, there will be a molecular orbital made up of the p-orbitals on the sulfur and both oxygens extending over and under the plane of the molecule which includes all three atoms/
2. C is correct. 
3. If the gas is expanding into a vacuum, then no work is being done (w = 0). And if the system is thermally isolated, the heat exchanged between the system and the surroundings is also zero (q = 0). Therefore, ΔE = q + w = 0 + 0 = 0, which would be answer B. Hope that makes sense!
Steve
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