Question

Iron shows variable valency whereas calcium does not. Explain.

Answer 1

Iron is a transition metal and it has configuration of 3d^​6 4s^​2 and it either loses two electron to show + 2 oxidation state or it losed three electron to show +3 oxidation state. Both these states are the most stable state. (valency 2,3)
Whereas Calcium is having 2,8,8,2. So after losing two electrons it get the stable 2,8,8 configuration which is a stable state. Thus the oxidation state of calcium is +2 (valency 2)