Can someone me out on this question ?
what is the name for that portion of the u.s constitution that explains the purposes of the united states government?
the articles
the preamble
the legislative branch
the declaration of independence

The answer you're looking for is the preamble.

Both of them are limits on the power of the government.

They are both written contracts of sorts that spell out what governments can and cannot do.

One major difference between these two documents is their purposes. The Magna Carta was made to prevent the angry populous from overthrowing the king. Unlike the U.S Constitution, which was simply made to set fair laws for all people in a new country