Answer: d. iodine and calcium
Explanation: Ionic bonds are formed by transfer of electrons between metal and non metals.
Covalent bonds are formed by sharing of electrons between non metals
Electronic configuration of calcium:
![[Ca]=[Ar]4s^2](https://tex.z-dn.net/?f=%5BCa%5D%3D%5BAr%5D4s%5E2)
Calcium atom will lose two electron to gain noble gas configuration and form calcium cation with +2 charge.
![[Ca^{2+}]={Ar]](https://tex.z-dn.net/?f=%5BCa%5E%7B2%2B%7D%5D%3D%7BAr%5D)
Electronic configuration of iodine:
![[I]=[Kr]4d^{10}5s^25p^5](https://tex.z-dn.net/?f=%5BI%5D%3D%5BKr%5D4d%5E%7B10%7D5s%5E25p%5E5)
Iodine atom will gain one electron to gain noble gas configuration and form iodide ion with -1 charge.
![[I^-]=[Kr]4d^{10}5s^25p^6](https://tex.z-dn.net/?f=%5BI%5E-%5D%3D%5BKr%5D4d%5E%7B10%7D5s%5E25p%5E6)
In calcium iodide the one electron from calcium metal gets transferred to iodine atom and thus form an ionic bond to give 