You answer this by using the pH formula and and the relation of pH and pOH, pH = -log[H+] and 14 = pH + pOH. The correct classification are as follows:
A. [H2O+]=6.0x10^-12
basic
B. [H3O+]=1.4x10^-9
basic
C. [OH-]=5.0x10^-12
acidic
D. {OH-]=3.5x10^-10
acidic
Hope this answers the question.
