Answer:
Cations are positively charged atoms and hence we need to make the atom positively charged in order to get a cation
We know that an atom is neutral as a whole, so we have equal number of electrons and protons
since we cannot mess with the number of protons in an atom, we have to do it by altering the number of electrons
If we reduce the amount of electrons in an atom, the net charge will be positive and hence a cation will be formed
Because the calcium ion donates two electrons to achieve the stable state. So the layer of electrons decrease form 4 layers(2,8,8,2) to 3 layers(2,8,8). Thus, the radius of a calcium ion is smaller than a calcium atom.
