Question

a scientist dissolved a white powder in water and noted that the resulting solution was acidic. why should the scientist not infer that the white powder contained hydrogen ions?
acids never contain hydrogen ions.
bases always contain hydrogen ions.
some acids do not contain hydrogen ions.
acids only contain hydroxyl ions.

Explanation:

According to the Arrhenius - acid base theory, acids produce hydrogen ions in solution. But according to the Lewis - acid base theory, some substances can act as acids without containing hydrogen ions. For example, metal ions like $Al^{3 + }$ can act as Lewis acids by accepting electron pairs. So just because a solution is acidic doesn't mean the original powder contained hydrogen ions as some acids (Lewis acids) do not contain hydrogen ions in the traditional sense.

Answer:

C. Some acids do not contain hydrogen ions.