Question

Four successive members of the first series of the transition metals are listed below for which one of them the standard potential $\left(E_{M^{2+}/M}\right)$ value has a positive sign?

• A. $Ni(Z=28)$
• B. $Cu(Z=29)$
• C. $Fe(Z=26)$
• D. $Co(Z=27)$

Answer 1

Answer: (B)

$Cu(Z=29)$

In the electrochemical series, $Cu$ is below hydrogen.
Hence, it has positive value of standard reduction potential $\left(E_{M^{2+}/M}\right)$.
The standard reduction potentials are given below.

$Ni(Z=28)$ - 0.257 V

$Cu(Z=29)$ + 0.337 V

$Fe(Z=26)$ - 0.440 V

$Co(Z=27)$ - 0.280 V