The first option best captures the differences in conversation styles between friends and a boss-employee dynamic. Friends, being more equal in social status, typically engage in informal discussions using slang and colloquial language, while a boss and employee use a more formal register, emphasizing proper grammar and clarity, often avoiding slang.
The other options contain elements that may not apply universally, such as the idea that friends only discuss personal topics or that boss-employee interactions must strictly avoid personal information. Additionally, while conversations among friends may be more fluid, it doesn’t account for all professional interactions being monotone or lacking facial expressions. Lastly, the duration of conversations can vary widely in both contexts; it isn't strictly defined by the relationships.
Thus, the differences in language register and formality are the clearest distinguishing factors.