Which species in each of the following pairs is better reducing agent under standard state conditions (`E^(@)` values are given ) ? Give reasons for your answer.
(a) `K_((s))(-2.93V) or Mg_((s))(-2.36V)`
(b) `Hg_((l))(0.86V) or Ni_((s))(-0.23)`

Explanation

Lower the standard reduction potential `(E_("red")^(@))` of a species, better is reducing agent.
(a) `E_("red")^(@) " of " K_((s) lt E_("red")^(@)` of Mg, hence `K_((s))` is a better reducing agent than `Mg_((s)).`
(b) `E_("red")^(@)` of `Ni lt E_("red")^(@)` of Hg, hence `Ni_((s))` is a better reducing agent than `Hg_((l)).`