Which of the following grants provides additional land for every three months of military service?

The correct answer pertains to the bounty grant. Bounty grants were specifically designed to incentivize military service by offering land in exchange for service provided. For every three months of military service, veterans were entitled to receive additional land, making this grant a form of compensation for their commitment to the armed forces. These grants were particularly significant during the period when land was being distributed in Texas, as they encouraged enlistment and rewarded those who had served.

In contrast, other types of grants, such as donation grants typically offered land without a service requirement and were often given to individuals for settling in certain areas. The Republic veterans donation grant is another form of support aimed at veterans, but it doesn't specifically tie the amount of land to the length of service in the same way that bounty grants do. Confederate scrip refers to a currency issue by the Confederate government and does not relate to land grants tied to military service. Thus, the bounty grant stands out as the correct answer due to its direct relationship with military service and land distribution.