Quinones are good electron acceptors, party because reduction restores aromaticity.

`Q+2e^(-)+2H^(o+)rarr H_(2)Q`
Give the decreasing order of `E^(c-)._(reduction)` of the following quinones `:`

Explanation

`a.` Decreasing order or `E^(c-)._(reduction):`
`IIIgtIgtII`
`b. IIIgtIIgtI" "c. IIgtI`
`a.` After reduction, products are `:`

Reactivity order `: IIgtIgtIII`
Stability order `: IIIgtIgtII`
`III` is more stable due to `+R(` or `+M)` effect of `Cl` than `+I` and `H.C.` effect of `CH_(3)`.
More stable the product means faster the reduction of quinone to hydroquinone and therefore higher `E^(c-)._(red)` value `:.` Decreasing order of `E^(c-)._(red)` value in `(a): IIIgtIgtII.`
`b.` Stability order `: IgtIIgtIII`
Reactivity order `: IIIgtIIgtI`
`(III)` is more easily reducedt to
because it generates two aromatic rings which have more resonance energy 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 .

The reaction is representes as follows `:`
`Q+2H^(o+)+2e^(-) rarr H_(2)O`
`:.` Reduction potential `(E^(c-)._(Q|H_(2)O)):IIgtI` .
`c.` Stability order `: IgtII`
Reactivity order `: IIgtI`
Standard reduction potential `(E^(c-)._(Q|H_(2)O)):IIgtI`

`(I)` has two individual benzene rings whose combined resonance energy along with that ot two `(C=O)` groups is more than the resonance energy of three benzene rings of reduced product `(I_(1))`.