Final answer:
The condenser is the part of the optical microscope that concentrates light on the sample(option c).
Step-by-step explanation:
The part of the optical microscope that concentrates the light being directed through the sample is the c)condenser.
The condenser lens is strategically placed just below the sample stage to focus light through the specimen. This process matches the aperture of the objective lens located above the stage. The condenser can be adjusted using the condenser adjustment knob to optimize the illumination of the specimen, supporting various techniques like brightfield and dark field illumination. The objective lens then magnifies the specimen, while the eyepiece further increases this magnification to present a clear, enlarged image to the observer.