Which species contain a dative covalent (coordination or coordinate) bond?

I.     Carbon monoxide, CO

II.     Ammonia, ${\text{N}}{{\text{H}}_{\text{3}}}$

III.     Oxonium ion, ${{\text{H}}_{\text{3}}}{{\text{O}}^ + }$

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B

One respondent would have preferred “hydronium” ion although the ion was made clear by the formula. Over half the candidates gave the correct answer.