Type of lens used as simple microscope
A. Binocular lens
B. Plano concave lens
C. Concave convex lens
D. Convex lens

Hint: The converging lens is required for microscope. Microscopes require the lens which can magnify small Objects placed under the microscope, such as the magnifying glass, eyepieces for telescopes and microscopes.

Complete answer:
Understand that the lens used in the microscope provides the magnification for the micro objects placed under the microscope.



Here, and are the focal point of the convex lens,
Closely placed object in front of the convex lens gets magnified to a very large image because the rays of light coming from the point object get parallel. Which results in the magnification of the micro object. The eye piece receives the magnified image of the object.
Therefore, the Convex can be used as a simple microscope.

Hence, the correct answer is option (D).

Additional information:
Define microscope: It is an instrument used to view the small objects. Such as insects, microorganisms, etc. The Commonly used lens to view the small objects is a convex lens.

Define convex lens: Spherical spheres are used to construct the optical lens. If those surfaces are bent outwards, the lens is called a convex lens. These types of lenses can converge a beam of light coming from outside. The distance between the principal foci and focal point is called the Focal length of the convex lens. In case if one of the surfaces is flat and the other convex, then it is called a Plano-convex lens.

Note: The convex lens is best used for the magnification of the micro objects and the compound arrangement of these convex lenses are used to increase the magnification of the microscope.