In many of the steps in the lab, a mixture was centrifuged and then decanted. In general terms, what is accomplished by these steps? In what kind of situation would these steps not be able to separate two compounds ?

to separate the compounds by gravity

Explanation:

Centrifuging is the process of separating compound in a liquid mixture by means of gravity and settling. This makes use of the density principle. In the process, the sample is added to the centrifuge. This is then rotated at a certain speed, say 50 rpm. The circular motion creates a force of gravity that pulls the compounds downwards. This then separate the compounds. The heaviest and most dense go down first, then the lighter particles on the top.  

it should be all of them because it asks if you included all of those in your answer

explanation:

answer; talc and gypsum;