The correct sentence is: "It is unprofessional on your side." Why? The preposition "on" is typically used when referring to someone's behavior, responsibility, or action. For example: * "That was a mistake on your part." * "The error was on their side." Using "from your side" is not natural in this context because "from" implies direction or origin rather than responsibility. However, "from your side" might work in other contexts, such as referring to a perspective: * "We expect a response from your side."