Eight states were admitted to the Union between 1820 and 1850 How many were free states?

That would be 4

Between 1820 and 1850, eight states were added to the Union: Maine (1820), Missouri (1821), Arkansas (1836), Michigan (1837), Florida (1845), Texas (1845), Iowa (1846), and Wisconsin (1848). Maine, Michigan, Iowa, and Wisconsin were free states, while Missouri, Arkansas, Florida, and Texas were slave states. This maintained the balance between free and slave states.