Question

drag the missing word into place
the scientists studied the of the soil to determine
how much fertilizer was in it.
element solvent
composition

Explanation:

The word "composition" means the combination of parts or elements that make up something. In the context of soil, studying its composition (what it is made of) helps determine the amount of fertilizer (a component) present. "Element" is too narrow as it refers to a single substance, and "solvent" (a substance that dissolves another) is not relevant here.

Answer:

composition