So I mixed some salts with sulfuric acidand then added potassium permanganate to them. Some of them change its to yellow and some of them took...

So I mixed some salts with sulfuric acid and then added potassium permanganate to them. Some of them change its to yellow and some of them took potassium permanganate color, which is purple. I have a post lab question says "The solution does not reduce an acidic solution of potassium permanganate" What does that mean? And how can I know?