Question

Four successive members of the first row transition elements are listed below with atomic numbers. Which one of them is excepted to have the highest $E^0{M}^{3+}/M^{2+}$ value?

• A. Co(Z=27)
• B. Cr(Z=24)
• C. Mn(Z=25)
• D. Fe(Z=26)

Answer 1

The correct option is A Co(Z=27)

Generally, standard reduction potential value increases from left to right in the period of d-block elements but there are some exceptions. Mn${}^{3+}$ and Co${}^{3+}$ behave as strongest oxidizing agent in aqueous solution. $E^{0}C{o}^{3+}/C{o}^{2+}$ = + 1.97V is highest suggesting thereby that Co${}^{3+}$ is most stable in aqueous solution. Thus, Co (Z=27) has the highest $E^{0}C{o}^{3+}/C{o}^{2+}$