Question

Four successive members of the first row transition elements listed below with atomic numbers. Which one of them is expected to have the highest $E_{m{^{3+}}/m{^{2+}}}^{\circ}$value?

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

Answer 1

Answer: (D)

$Co (Z = 27)$

Answer 2

SRP value normally increases from left to right in the period of rf-block elements. Some SRP value are exceptionally higher due to stability of product ion. e.g.
$\, \, \, \, \, \, \, \, \, \, \, E_{m{^{3+}}/m{^{2+}}}^{\circ} = +1.57 V; E_{Co{^{3+}}/Co{^{2+}}}^{\circ}=+1.97 V$
Thus, $E_{m{^{3+}}/m{^{2+}}}^{\circ}$ is highest for Co.