Individual chromosomes become distinct through a light microscope during this mitotic stage

The correct option is Prophase.

To understand why this is the case, we can break down the events of mitosis step-by-step:

During the interphase preceding mitosis, the cell's genetic material exists as a loose, uncoiled, and diffuse network of fibers called chromatin. In this state, individual chromosomes are extremely thin and long, making them completely indistinguishable from one another under a standard light microscope.

As the cell enters prophase, the first official stage of mitosis, several key events occur:
1. Chromatin Condensation: The diffuse chromatin fibers begin to tightly coil, condense, and fold. This process makes the chromosomes much shorter, thicker, and highly packaged.
2. Visibility: Because of this intense condensation, the chromosomes become compact enough to bend and scatter light, allowing them to finally become distinct and visible as individual structures under a light microscope.
3. Structure: Under magnification, each duplicated chromosome can be seen to consist of two sister chromatids joined together at a region called the centromere.

In subsequent stages like metaphase, anaphase, and telophase, the chromosomes undergo further alignment, separation, and decondensation, but the initial transition from invisible chromatin threads to distinct, recognizable chromosomes occurs specifically during prophase.