What is the first stage of mitosis where chromosomes become visible?

During prophase, the first stage of mitosis, chromatin condenses into distinct visible chromosomes. This process is crucial for cell division, as it allows the chromosomes to be organized and managed effectively as the cell prepares to divide. Each chromosome is made up of two sister chromatids, which are joined at the centromere.

As prophase progresses, the nuclear envelope begins to break down, and the spindle apparatus starts to form. The visibility of chromosomes at this stage is important because it sets the stage for the proper alignment and separation of the chromosomes in the subsequent phases of mitosis. The ability to see individual chromosomes is a key defining feature of this stage, making prophase the correct answer to the question.