The following reactions are involved when Cr²⁺ and Fe²⁺ act as reducing agents.

Cr²⁺⇒ Cr³⁺ (E^⁰_{Cr3+/ Cr2+} = - 0.41 V)

Fe²⁺⇒ Fe³⁺ (E^⁰_{Fe3+/ Fe2+} = +0.77 V)

Since, Cr has less potential value, Cr²⁺ gets oxidised easily than Fe²⁺. Therefore, Cr²⁺ is a better reducing agent that Fe³⁺.