Which of the following does NOT occur during mitosis? a) Centromeres split, b) chromosomes replicate, or c) spindles form?

The answer is b) chromosomes replicate

DNA replication occurs before mitosis. So, duplicated chromosomes are already present in mitosis. They are connected by centromeres. During different phases of mitosis, spindles are formed and pull chromosomes toward the opposite poles of the cell so centromeres must split.