Which of the following is not an electrophile?

Identify the correct order of leaving group ability for the given leaving groups:

(I) ${\mathrm{OH}}^{-}$
(II) 
(III) ${\mathrm{CH}}_3{\mathrm{COO}}^{-}$
(IV) ${\mathrm{CH}}_3{\mathrm{SO}}_3^{-}$