Explanation: Under GMDSS (Global Maritime Distress and Safety System), survival craft stations equipped with MF/HF radios are required to be capable of Digital Selective Calling (DSC) for distress alerting. The international MF (Medium Frequency) DSC distress frequency is 2187.5 kHz. While direct radiotelephony (voice) distress communication typically occurs on 2182 kHz, GMDSS equipment for survival craft *must* be able to transmit and receive on 2187.5 kHz for the initial digital alert. This capability is a core characteristic of GMDSS-compliant equipment, as DSC is the primary method for initiating a distress call in the MF band, which then prompts follow-up voice communication. The other options are incorrect: * **490 kHz** and **518 kHz** are NAVTEX frequencies for navigational warnings, not distress radiotelephony. * **4209.5 kHz** is an HF (High Frequency) DSC distress frequency, applicable to different GMDSS sea areas (A3/A4), but 2187.5 kHz is the primary MF DSC frequency covering sea area A2 and beyond, making it a more fundamental characteristic for typical survival craft MF/HF equipment.