Elimination of HCl from isomeric chlorocyclohexadienes Which of these is most easily dehydrohalogenated?

a. 5-Chlorocyclohexa-1,3-diene (1)
b. 3-Chlorocyclohexa-1,4-diene (2)
c. 1-Chlorocyclohexa-1,4-diene (3)
d. Both 1 and 3

I encountered this question a while ago.  The given answer is option (b) (compound 2). But the dehydrohalogenation of compound 1 produces benzene which has high heat of formation. So why isn't that the answer?
That's a fair question,

Assuming that you use a strong base for dehydrohalogenation you will be deprotonating the most acidic $\ce{H}$ resulting in formation of a carbanion which has the highest stability in compound number 2 

You can see that the carbanion formed in compound numer 1 will have resonance with only one of the double bond and hence will be less stable then the carbanion in the compound 2 which has resonance from both the double bond.

Mechanism can be as follow :-



Also;