It can be concluded that the intended purpose of the missouri compromise was to a. give the free states more votes in the electoral college than the slave states. b. keep the balance of power in the senate between the slave states and free states. c. change the balance of power given to the free states and slave states in the constitution. d. allow the slave states to have more influence in the house of representatives than the free states.

 B. keep the balance of power in the Senate between the slave states and free states.

Further detail:

 The Missouri Compromise (1820) admitted Missouri into the Union as a slave state with Maine being added at the same time to keep the balance of slave and free states equal.  It also prohibited any future slave states north of the latitude line 36 1/2 degrees north of the equator in territories of the Louisiana Purchase, with the exception of Missouri (north of that line) being admitted as a slave state.  

B. keep the balance of power in the Senate between the slave states and free states.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.