How would you compliment a counterpart by saying he is a good boy in Arabic?

The correct response, which translates to "a good boy" in Arabic, is "amal mumtaaz." This phrase effectively conveys a positive compliment, indicating that someone is excellent or outstanding in their behavior or character.

The other phrases do not serve the specific purpose of complimenting someone in that particular context. "Shukran" simply means "thank you," which is used to express gratitude rather than to compliment someone's character. "Ahlan wa sahlan" translates to "welcome," and is typically used to greet someone rather than to make a personal commendation. "Mabruk," on the other hand, means "congratulations," which is appropriate for celebrating achievements but does not necessarily convey the sentiment of being a "good boy." Thus, "amal mumtaaz" is the most suitable choice for complimenting someone in that manner.