Which of the following reagents is used to remove complexed metals?

Calcium hydroxide is commonly used to remove complexed metals because it acts as a hydroxide source. It can precipitate certain metal ions by forming insoluble metal hydroxides, effectively removing them from the wastewater. This precipitation process is particularly useful for metals such as lead, copper, and zinc, which can form stable complexes with other ions in solution. When calcium hydroxide is added to the wastewater, it raises the pH and encourages the formation of these metal hydroxides, facilitating their removal through sedimentation or filtration.

On the other hand, hydrochloric acid typically dissolves metals rather than removing them; ammonium nitrate does not have a strong role in metal removal and is more commonly associated with nitrogen-based nutrient management; and glycolic acid is mainly used in different contexts, such as in cosmetic chemical peels or as a solvent, rather than for removing metals in wastewater treatment.