What test is used to compare soil samples using equal amounts of soil samples (a control and unknown) and placed in varying levels of liquids?
a) titration test
b) ultraviolet test
c) density gradient tube test
d) comparison microscope test

I think the correct answer would be the density gradient tube test. This is used not only but also in other solid materials in order to determine the composition or the substances in the mixture. Hope this answers the question. Have a nice day.

29.1-12=17.1the answer is this one