The answer key for Realidades Level 2 is included as part of the Teacher's Edition. There are three editions of Realidades 2: one from 2004, one from 2008 and a 2014 digital edition. The answers to each are found in the corresponding Teacher's Editions.
The Realidades books are published by Pearson Education as part of its Spanish curriculum. This curriculum covers Spanish levels 1-4. Realidades 2 is designed for the second year of Spanish studies, and it includes many practice exercises in each chapter. While anyone may purchase the student editions of these textbooks, only teachers have access to materials that include the correct answers for each exercise.