Which of the following did the wilmot proviso provide for?
it extended the 36°30' line to the pacific ocean.
it allowed states north of the line to be slave.
it prevented slave states in land gained from mexico.
it forced texas to give up some of its land to pay debts.

The subject of the Wilmot Proviso was slavery, and more specifically, slavery in the lands newly gained from Mexico (California, Nevada, Arizona, etc). According to this proviso, slavery was to be banned in the newly acquired territory, so the correct answer is

It prevented slave states in land gained from Mexico.

however, the Proviso did not become law and was finally rejected in the compromise of 1850.