Smelting Daily Question 9.4

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1. Please hide your replies; editing after posting is ineffective! Delete directly without hiding! 2. Hiding method: http://bbs.hcbbs.com/thread-492556-1-1.html 1 B9 S# i( J3 \+ }8 J1 \ a 3. 5 points for correct answers; there is a reward for everyone who participates. For multiple-choice questions, the testing method to determine whether gold is still present in the tail liquid after recovering gold from gold-containing aqua regia using a reducing agent – that is, to check if the gold has been completely recovered – which of the following methods can be used? Please select the correct answer number: 1 Judge based on the color of the residual liquid; if the residual liquid has a color, it indicates that the gold has been completely precipitated and extracted. 2 Test using an acidic stannous chloride solution; if the solution turns purplish-red, then gold is present in the solution; otherwise, the gold has been completely precipitated and extracted. 3 Judge based on pH. 2