The admission of missouri as a slave state was controversial in the senate because

c. it would upset the balance

Explanation:

The idea of the federation and the Union of the States was to eventually abolishing slavery, all of the efforts were to bring the pro-slavery states to an agreement unti abolishing slavery, and the forces between pro-against slavery states was fairly balanced, adding Missouri to the Union would mean that the senate approved the anexation of slavery states and miss-balancing the pro vs against slavery states.

what

Explanation:

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