How would you account for the following:

Of the d4 species, Cr²⁺ is strongly reducing while manganese (III) is strongly oxidizing.

The +2 oxidation state becomes more stable on moving across a period i.e. the tendency of metals to give electrons becomes more. Therefore, vanadium(II) oxide and chromium(II) oxide are strong reducing agents.

As if the value of electrode potential is higher i.e. more energy required to withdraw an electron from an isolated atom, more readily it can be reduced and lesser the electrode potential more readily it can be oxidized.

The electrode potential of Cr³⁺│ Cr²⁺is negative so it acts reducing agent or can undergo oxidation which makes it a more stable ion while that of Mn³⁺│ Mn²⁺ is positive and it undergoes reduction acts as strong oxidizing agent. Also, Mn³⁺ has an exactly half-filled d- orbital which is highly stable.