The largest normal metaphase chromosome has a size of
A. 1μm
B. 10μm
C. 20μm
D. 30μm

Hint: Metaphase chromosome is a chromosome at the point of the cell cycle (the chain of events in the life of a cell) where the chromosome is more compact and easy to discern and thus to analyze. Metaphase chromosomes are often used for karyotyping and chromosome analysis so they can be readily seen.

Complete answer: With the base of the nucleosome central particle consisting of 146 base pairs of DNA, the largest normal metaphase chromosome has a radius of 30 nm. When a chromosome at its most compact form can vary in size from 130,000 base pairs in the endosymbiotic bacteria during the metaphasic state, so the chromatin can be further condensed by coiling in fibres to 30nm. One of the key methods of classical cytogenetics and cancer research is the study of metaphase chromosomes. Chromosomes are compact in metaphase (thickened) and highly coiled, making them more appropriate for visual examination. The classical image of chromosomes is created by metaphase chromosomes (karyotype). Cells are cultivated in short-term culture for classical cytogenetic studies and arrested using mitotic inhibitors in the metaphase. They are also used under a microscope to study the arrangement and number of chromosomes for slide preparation and banding (staining) of chromosomes to be visualized (karyotype).
So, the correct answer is option D.

Note: During prometaphase and metaphase, one of the cell cycle checkpoints happens. The cell reaches anaphase only after all chromosomes have been associated at the metaphase plate when each kinetochore is correctly connected to a bundle of microtubules.