Detailed Instructions: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Q: Question: The determination of cyanide by the Liebig method is based on the addition of a silver nitrate standard solution:
Options: <1> Until complete precipitation of silver cyanide. <2> Until the precipitation of silver cyanide begins. <3> Until the appearance of a red precipitate of silver chromate. <4> Until the AgCN complex is quantitatively formed. <5> Until the precipitation of silver iodide, yellow.
A:
2