In a titration of aqueous NH₃ with 0.100 M HCl, the equivalence-point pH is approximately 5.6. The student nevertheless uses phenolphthalein (transition range 8.3–10.0) and ends the titration when the faint pink color just disappears. How will this choice most affect the calculated concentration of NH₃?
a) It will be unaffected because the indicator error cancels when the calculation is performed.
b) It will be overestimated because too little HCl is added at the endpoint.
c) It will be underestimated because too little HCl is added at the endpoint.
d) It will be underestimated because too much HCl is added at the endpoint.