Khan Academy C/P Passage Help

[LIC2015]

The passage titled "Quantitative Analysis of Contaminated Water Supply" is absolutely tearing me apart (link below). I'm totally confused about the questions. The hints aren't particularly helpful in this instance. Can someone help interpret Table 1 and why this technique works, as well as the questions and why the answers make sense? Would really appreciate it.

https://www.khanacademy.org/test-prep/mcat/physical-sciences-practice/physical-sciences-practice-tut/e/qualitative-analysis-of-contaminated-water-supply

 

[wizzed101]

The technique is based on the fact each group of cation has different solubility when in conjunction with certain anion.
Ex: Pb2+ will precipitate with Cl- while Na+ & Cu2+ will not. By testing first with HCl, it can be deduced that the solution contain Pb 2+. To test for present of Cu2+ and Ny, CO32- can be used etc...
So you need to know which salt is normally soluble.
As for the answers, the crux is Le Chatelier's. You should also know colors and smells of common gases. The UV is straight forward: it absorbed redish so it must've been blue-green.