Mexico experienced a series of liberal reforms in the 1860s instituted by
santa anna.
benito juarez.
porfirio diaz.
lázaro cárdenas.

Let's look at the times when each of the listed reigned and see which one did so in 1860s:

General Santa Anna was the president of Mexico several times (with interruptions) but last time in 1855 - so that couldn't be him

Benito Juarez - he was the president 1857-1872. - the whole of 1860. This is the correct answer, and Benito Juares is in fact known for his reforms, and remembered with fondless in Mexico. His reign is known as la Reforma - the reform

Porfirio Diaz governed 1976-1915, so definitely not in 1860s, and Lazaro Cardenas governed even later.