Question

Justify the statement:

If \[\ce{E^{\circ}_{{M^{n+}/{M}}}}\] is positive, Mⁿ⁺ can be reduced to M by H₂ gas under standard conditions.

Answer 1

If \[\ce{E^{\circ}_{{M^{n+}/{M}}}}\]​ is positive, it means that Mⁿ⁺ ions have a greater tendency to get reduced than H⁺ ions.
Therefore, H₂ gas cannot reduce Mⁿ⁺ to M under standard conditions.
Instead, Mn⁺ ions can oxidise H₂ gas to H⁺, and themselves get reduced to M.