In an amperometric titration for chlorine residual using PAO (Phenylarsine Oxide), what specific change in the electrical circuit indicates that the titration endpoint has been reached?

• The microammeter needle deflects rapidly upwards (increases current)
• The digital display flashes a red warning light
• The sample liquid suddenly changes from pink to clear
• The microammeter needle ceases its downward deflection (current stops decreasing)