Comment of the following observations :
`E^("ϴ")` for `M_((aq))^(2+) +2e^(-) to 2e^(-) to M_((s))` (where, M = Ca, Sr or Ba) is nearly constant.

Explanation

Electrode potential `(E^(0))` of any `M_(2)^(2+)//M` electrode depends upon three factors : (i) Ionization enthalpy (ii) Enthalpy of hydration, (iii) Enthalpy of vapourization.
The combined effect of these factors is approximately the same for Ca, Sr, and Ba. Hence, their electrode potentials are nearly constant.