Question
Siti is in charge of a gimmick to launch the Science Week in school. She has prepared a white cloth that is written with 'Science Week 2020 ’ on it using lead(II) nitrate solution. During assembly, the headmaster invited her to spray solution Q onto the cloth and the invisible words suddenly appear to be yellow in colour. What is the solution Q sprayed onto the cloth?
A Zinc nitrate
C Potassium iodide
B Barium nitrate
D Magnesium nitrate
Solution
Hello! Basically this question is asking, which of the 4 salts will react with Pb(NO_3)_2 to produce a yellow precipitate? All inorganic nitrates salts are soluble, so options A, B and D are out. Answer is C because potassium iodide reacts with lead(II) nitrate to produce a yellow precipitate, PbI_2, lead(II) iodide.
PbI_2 looks something like this if you have chance to do it in your school’s chemistry lab:
Hope this helps! 
I see Thank you very much!
