The correct option is
D metaphase
Morphology of the chromosomes refers to the external structure, form and size of chromosomes.
Mitosis is a type of cell division in which a parent cell divides and forms two daughter cells that are identical to one another and to the parent cell. They carry the same number of chromosomes and the same types of chromosome as the parent cell. Mitosis involves karyokinesis or the division of the nucleus followed by cytokinesis or the division of the cytoplasm
Karyokinesis involves four phases. They are prophase, metaphase, anaphase and telophase.
In interphase, the DNA associated with histone proteins form dense string-like fibres called chromatin.
During the prophase phase of mitosis, the chromatin undergoes coiling and packaging to form into compact, short structures known as chromosomes. This is called condensation and it starts in prophase and gets completed by the end of the next phase, the metaphase.
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In metaphase, the chromosomes are clearly visible and each chromosome has two chromatids. Hence , the morphology of chromosomes can be best studied during metaphase.