Plz help I will mark you brainlist plz

Explanation:

Hey there!

Your required answer is option A.

The reason is, Pure substances will always be elements or compounds.

Compounds are the pure substance made up of elements in a fixed proportion.Elements are the pure substance made up of only one kind of atom.

And, Mixture are mainly of two type,

Heterogeneous mixture : Which easily defined as the type of mixtures which can be seen through our naked eye. Homogeneous mixtures: The type of mixtures which can not be seen through our naked eye is called homogeneous mixtures.

Hope it helps..

B.) nitrogen fixationnitrogen fixation is the process of nitrogen molecules seeping into the soil and inside plant roots and bacteria. it gives more "life" to plants

Ascientist will use that to figure out how or why things are the certain way they are i hope this