Out of the given options, the best expression to use at the end of the conversation with your new boss would be "Encantada."
"Encantada" is a Spanish expression that translates to "Nice to meet you" or "Pleased to meet you" in English. It is a polite and respectful way to end the conversation, showing your appreciation for the introduction and conveying a positive impression.
While the other options ("¿Qué tal?", "¿Cómo estás?", and "Hola.") are commonly used greetings in Spanish, they may not be as suitable for concluding a conversation with a new boss. These expressions are more appropriate for initiating a conversation or addressing someone casually.
By using "Encantada," you demonstrate professionalism and respect towards your new boss, establishing a friendly tone while still maintaining a level of formality.