The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizing power of the cationic species, ${\text{K}}^{+},{\text{Ca}}^{2+},{\text{Mg}}^{2+},{\text{Be}}^{2+}$?

According to Fajan's rules, the polarizing power of a cation increases with an increase in its charge and a decrease in its size.Charge: ${\text{Ca}}^{2+},{\text{Mg}}^{2+},{\text{Be}}^{2+}$ ($+2$) have higher polarizing power than ${\text{K}}^{+}$ ($+1$).Size (for the same charge): Among the $+2$ ions, the size order is ${\text{Be}}^{2+}<{\text{Mg}}^{2+}<{\text{Ca}}^{2+}$.Therefore, polarizing power order is ${\text{Be}}^{2+}>{\text{Mg}}^{2+}>{\text{Ca}}^{2+}$.Combined order: ${\text{K}}^{+}<{\text{Ca}}^{2+}<{\text{Mg}}^{2+}<{\text{Be}}^{2+}$.