Question

what was the main reason for the inclusion of the fugitive slave law in the compromise of 1850?
to reward slave states for contributing funds to settle land claims
to foster support for the admission of another free state
to pacify the free states for the decision to maintain slavery in the nation’s capital
to address problems caused by allowing popular sovereignty in the territories

Explanation:

The Compromise of 1850 aimed to balance tensions between free and slave states. California was admitted as a free state, which upset slaveholding states. The Fugitive Slave Law was included as a concession to slave states to gain their support for California's admission as a free state, preserving the sectional balance in Congress temporarily.

Answer:

B. to foster support for the admission of another free state