All titrant has drained out of the buret, into the reaction flask...
Answer: A) Discard the solution and begin the titration again.
The buret is only calibrated to the 50.00 mL mark, so any
volume of liquid past this mark cannot be measured. Since the
volume of titrant added to the flask cannot be determined accurately, the solution
must be discarded and the titration begun again.
Note: In practice, if more than 50 mL of titrant are needed
to reach the endpoint, the solution may have been prepared incorrectly.
If indicator is needed for the titration, check to see if indicator was added to the solution.