Which act provided land grants for the construction of transcontinental railroads?

The Pacific Railway Act is the correct choice because it specifically authorized the construction of the transcontinental railroad and provided land grants to the railroad companies to facilitate this construction. Signed into law in 1862 and later amended, the Act was aimed at encouraging the expansion of railroads across the United States, providing allocation of public lands to assist in the building of the railway lines.

The Homestead Act, while significant for promoting settlement and agriculture in the West by granting land to individuals, did not directly concern railroad construction. The Land Ordinance Act focused on the organization and sale of land in the Northwest Territory rather than railroads. The Interstate Commerce Act was primarily concerned with regulating railroad rates and practices after the railroads were established, rather than providing grants for their construction.