When would formation of a derivative be a necessary step in this experiment?

The formation of a derivative may be a necessary step in the experiment lies in the importance of the derived structure. Often the derivation product confers to reaction pathways which uses less reactive starting materials and more easily proceeds to completion. This also allows us to take a small amount of sample. The derivative may be a general compound allowing easy analysis. Often we encounter a product but we find it difficult to analyse it in ways we want. So the importance of forming a derivative which often are simpler compounds allowing easier analysis and having a similar functional groups and structural properties. Also sometimes we encounter problems when our desired product is unstable and forms stable degraded products. But if we somehow manage to synthesize a derivative it may be relatively stable and form no degradation products. It would be stable at least for a larger period of time making it easier to study its properties.  When we encounter problems similar to those mentioned above it becomes necessary for a researcher to form rather synthesize a derivative.

The correct answer would be 1. precipitation

C: plants and animals