Give the decreasing order of stability of the following quinones:
a.
b.

Explanation

a. Stability order: I gt II gt III
Reactivity order : III gt II gt I
(III) is more easily reduced to
because it generates two aromatic rings which have more reasonance ehergy and greater stability than the reaction of (I) and (II), which would generate only one benzene ring. Both (I) and (II) on reduction give one benzene ring. but (II) is less stable (more reactive) than I because adjacent `(C=O)` groups in (II) make it less stable.
(I)
(II)
(III)
The reaction is represented as follows: `Q + 2H^(+) + 2bar e rarr H_(2)O`
Therefore, reduction potential `(E_(Q//H_(2)Q)^(@))` : II gt I
(I)
(I) has two individual benzene rings whose combined resonance energy (R.E.) along with that of two `(C=O)` group is more than the R.E. of three benzene rings of reduced product `(I_(1))`.