Most environmental colloids have a negatively charged surface at pH 7 due to their lower pHo values. Which one of the following statements is true? a) pHo decreases in the presence of a low concentration of NaClO4. b) pHo fluctuates in the presence of a moderate concentration of NaC104. c) pHo increases in the presence of a high concentration of NaClO4. d) pHo stays constant, independent of the NaClO4 concentration. e) None of the above