Suppose that biuret reagent turns purple when it is added to an unknown substance. what can you conclude about the substancea. the substance is a acidb. substance contains proteinc. substance contains starchd. none of the above are valid

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

qualitative observation deals with data that can be observed with our senses: sight, smell, touch, taste, and hearing. they do not involve measurements or numbers. for instance, colors, shapes, and textures of objects are all qualitative observations.