chemistry question

The key is "It forms H₂S when acidified." It must contain S²⁻ ion, Only ans B is possible.

The cation of answer B is NH₄⁺, It will not form ppt. with all the mentioned anions. since ammonium salt are all soluble.

睇唔明這句 "hydroxide同ammonium應該是會form precipitate,potassium反而不會" 是什麽意思。

Answer C is KBr which cannot give foul smell when acidified.

2013-10-27 01:27:14 補充：
ALL salts of K⁺, Na⁺, NH₄⁺ are soluble.