Final answer:
The microscope's ability to show two separate entities as distinct is called resolution. It is critical for clarity and detailing of an image, and superior to magnification which only enlarges the image. Therefore, correct answer is a.
Step-by-step explanation:
The characteristic that refers to the microscope's ability to show two separate entities as separate and distinct is known as resolution.
Resolution is the ability of a microscope to distinguish two adjacent structures as separate; the higher the resolution, the better the clarity and detail of the image. This is different from magnification, which is the ability of a lens to enlarge the image of an object when compared to the real object.
When working with light microscopes, especially at high magnifications such as 1,000 times with oil immersion lenses, resolution becomes critically important for studying the smaller details of cells like most prokaryotic cells.
Good resolution is essential because it determines how close two points can be to each other and still be visibly distinguishable. Without adequate resolution, even if an object is magnified, it may still appear as a blur.