Which compounds contain both ionic and covalent bonding?

I.     \({\text{CaC}}{{\text{O}}_{\text{3}}}\)

II.     NaCl

III.     NaOH

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B

This was thought to be a fair question despite one respondent’s worry that there would be ambiguity for candidates who believe NaCl has a small degree of covalency. 78% gave the expected answer.