Answer: Option (a) is the correct answer.
Step-by-step explanation:
A formula that represents how atoms are linked or joined together is known as a structural formula.
For example, the model given in the image (in question) represents arrangement of all the atoms. Therefore, it is a structural formula.
Whereas a chemical formula represents a compound along with ratio of compounds.
A space filling model and a ball-stick model is a three dimensional model. In space filling model atoms are represented by spheres whereas in ball stick model atoms are represented by ball and bonds are represented by stick.