The correct option is D Ca2+ ion has a noble gas electronic configuration and the Cd2+ ion has a 18e− electronic configuration in the outer shell
Ca2+:[Ar] → noble gas configuration
Cd2+:1s2 2s2 2p6 3s2 3p6 4s2− 3d10 4p6− 4d10−
Cd2+:[Kr]4d10 → 18e− electronic configuration
The outer most d-orbital cannot shield the nuclear charge as much and hence, the polarisation of Cd2+>Ca2+.