Final answer:
Histone H3 is the histone that is modified in the centromeric region of a chromosome, providing attachment sites for microtubules.
Step-by-step explanation:
The histone that is modified in the centromeric region of a chromosome, providing attachment sites where the microtubules will associate with the chromosome, is Histone H3. Histones are proteins that help in the packaging of DNA into chromatin. Histone modifications, such as acetylation or methylation, can affect the structure of chromatin and control gene expression. In the centromeric region, the modification of Histone H3 plays a role in the attachment of microtubules during cell division.