Answer: Spindle fibers are attached to their centromeres in metaphase.
Chromosomes are formed during the prophase of mitosis, in this phase nucleus disappears, formation of spindle fiber takes place and chromosomes are formed from the condensed DNA which is then followed by the alignment of spindle fibers on the equator of the cell to get attached with their centromeres, alignment followed by the attachment of spindle fibers to their centromeres occurs in metaphase.