Explanation: The allowed frequency tolerance for DSC (Digital Selective Calling) carrier frequencies is **10 ppm (parts per million)**. This standard is crucial for ensuring the reliable operation of DSC, especially in marine radio communications (GMDSS). DSC utilizes precise digital signaling, and accurate carrier frequencies are vital for proper modulation and demodulation of the data. A tolerance of 10 ppm ensures that the transmitting and receiving equipment can maintain synchronization and successfully decode the digital messages, preventing errors that could lead to missed distress calls or miscommunication. This requirement is established by international regulations and recommendations, such as ITU-R M.493. While specific frequency bands might also mention an absolute Hz value (e.g., 10 Hz), 10 ppm is the overriding requirement for MF/HF DSC transmitters, as it provides a consistent relative stability across the entire frequency range. Options A and B are fixed Hz values which are not universally applicable across the wide range of DSC carrier frequencies. Option C (5 ppm) is a tighter tolerance than required; 10 ppm is the maximum allowed.