As a result of the Mexican-American War, Mexican citizens living in the Mexican Cession

1) had to return to Mexico.

2) could become US citizens.

3) were separated from their families in Mexico.

4) declared their independence.

5) faced legal and social discrimination.

2) could become US citizens.

3) were separated from their families in Mexico.

5) faced legal and social discrimination.

Explanation:

The Treaty of Guadalupe-Hidalgo was the treaty that formally concluded the Mexican War (1846-1848) between the United States and Mexico. The main agreement established was the "Mexican Cession," the region that Mexico was forced to cede to the United States. It was agreed that Mexican citizens in that area would be considered as legal U. S. citizens unless they vacated the area or filed as Mexican citizens for that first year. In practice, this meant that many people were separated from their families, and a long process of discrimination against Mexican Americans started.

I believe 3 is the answer, because I think the U. S bought a part of Mexico.