Assertion (A): Cr^2+ is a strong reducing agent whereas Mn^3+ is a strong oxidising agent in aqueous solution. Reason (R): Cr^2+ -> Cr^3+ leads to the stable t_2g^3 (d^3) configuration, while Mn^3+ -> Mn^2+ leads to the stable half-filled d^5 configuration.

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A

JEE Advanced levelSingle correct optionDifficulty 3 of 3df040

Assertion (A): $Cr X^{2 +}$ is a strong reducing agent whereas $Mn X^{3 +}$ is a strong oxidising agent in aqueous solution. Reason (R): $Cr X^{2 +} Cr X^{3 +}$ leads to the stable $t_{2 g}^{3}$ ( $d^{3}$ ) configuration, while $Mn X^{3 +} Mn X^{2 +}$ leads to the stable half-filled $d^{5}$ configuration.

E^{\circ} (Cr X^{3 +} / Cr X^{2 +}) \approx - 0.41 V

and

E^{\circ} (Mn X^{3 +} / Mn X^{2 +}) \approx + 1.5 V

, so A is true.

Cr X^{3 +}

(

d^{3}

) is stabilised by the half-filled

t_{2 g}

set in an octahedral field, and

Mn X^{2 +}

(

d^{5}

) by the half-filled subshell. R is true and explains A.