Answer:
To decide for themselves whether to become a slave state or a free state.
Step-by-step explanation:
Generally, popular sovereignty is a term that describes the tenet in which a state, nation, or country's power is defined and maintained by the people of that particular place.
Hence, in this case, since Compromise 1850 is about the issue of slave or free state in the United States. The meaning of Popular Sovereignty here simply means that the Utah Territory and New Mexico Territory were given the option "To decide for themselves whether to become a slave state or a free state."