The correct answer is A: At the 12 volt battery chassis ground. The negative power return (ground) of a mobile transceiver should be connected at the 12-volt battery chassis ground or directly to the battery negative terminal. This provides the best ground connection and minimizes ground loops and interference. Connecting the negative lead directly to the battery or battery ground ensures a low-resistance path for return current. This is important because the negative lead carries the return current, and any resistance in this path can cause voltage drop and potential interference issues. Connecting to the battery ground (or battery negative terminal) provides the most direct, low-resistance connection, which is essential for proper operation and minimizing RF interference.