Final answer:
Frederick Douglass felt intensely happy when he saw Mrs. Auld smiling at him, signaling a major positive change in his life.
Step-by-step explanation:
The action that made Frederick Douglass intensely happy when he arrived at his master's new home in Baltimore was a Mrs. Auld smiling at him. In his narrative, Douglass describes the moment he met Mrs. Sophia Auld, his new mistress, and the overwhelming sense of rapture he felt upon seeing her kind expressions.
This event marked a profound change in Douglass's life, setting him on a path of learning and ultimately, freedom and self-actualization.