Final answer:
Interphase chromosomes cannot be discerned by light microscopy because they are not condensed during that phase. Instead, chromosomes are most visible during metaphase of mitosis when they are condensed and aligned.
Step-by-step explanation:
All except which of the following chromosomes can be discerned by light microscopy? The correct answer is b. Interphase chromosomes. Chromosomes are most easily observed during metaphase of mitosis, when they are condensed and aligned at the metaphase plate. Interphase chromosomes, however, are in a relaxed state and not condensed enough to be discerned with a light microscope. In contrast, polytene chromosomes, commonly found in certain insect cells like Drosophila salivary glands, and lampbrush chromosomes found in oocyte cells of vertebrates during meiosis, are large enough to be seen with a light microscope.
The individual chromosomes become visible with a light microscope during c. metaphase stage of mitosis. This is when the chromosomes are the most condensed and hence the most visible under light microscopy.