c) Magnifying power of a simple microscope is inversely proportional to the focal length of the lens. What then stops us from using a convex lens of smaller and smaller focal length and achieving greater and greater magnifying power ?

Explanation

c) The oretically, it is true. However, when we decrease focal length, abervations both spherical and chrmotic become more pronounced. Further, it is difficult to grind lenses of very small focal lengths.