Four successive members of the first series of transition metals are listed below. For which one of the of standard potential `(E_(M^(2+)//M)^(@))` value has a positive sign ?

Options

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

Answer

D

Explanation

The `E^(Theta) (M^(2+)//M)` value for copper is positive `(+ 0.34 V)` on account of following factors:
(i) high enthalpy of atomisation:
`Cu(s) rarr Cu(g)`
(ii) high second ionization enthalpy:
`Cu^(+)(g) rarr Cu^(++) (g)`
(iii) low enthalpy of hydroation:
`Cu^(++) (g) rarrCu^(++) (aq)`