Why did california's application for statehood cause an uproar?

The admission of California would upset the balance of power in the Senate between the Southern slave states and the Northern free states. In other words, The admission of California would give the Northern free states two more votes in the senate than the Southern Slave states. before the admission of California, the number of senators were equal between the sectional interests.

The answer b is correct this all occurred during the red scare