In the following multiple-choice questionnaire, $H_3O^+$ is often abbreviated by $H^+$(aq) or even $H^+$ ( which is quite wrong, because $H^+$ is always hydrated in the water! )
Which of the following is NOT a strong acid?
a) $HCl$ b) $HSO_4^-$ c) $HNO_3$ d) $H_2SO_4$
b) is correct