The elements of same group are placed in same group as they have similar properties. So Calcium is the element which resembles Mangesium.
Calcium and Magnesium both are alkaline earth metals.
They have similar properties as they have similar outer or valence shell electronic configuration
The general electronic configuration of alkaline earht metal is ns2
The electronic configuration of Mg [atomic number 12] and Ca [atomic number 20] are
![[Ne]3s^{2}](https://tex.z-dn.net/?f=%5BNe%5D3s%5E%7B2%7D)
and ![[Ar]4s^{2}](https://tex.z-dn.net/?f=%5BAr%5D4s%5E%7B2%7D)
respectively.
The first one because some people might not believe that and others might believe that.
Ionization energy is the measure of the extend to which the nucleus attracts the outermost electron
if ionization energy us high than force of attraction Is high so it is not easy to remove and vice versa .
hope you understand.....
An electron is smaller than a proton. An electron has the opposite charge of a proton. An electron is outside the nucleus, while a proton is part of the nucleus.
