What is the purpose of a SIM card in mobile devices?

A SIM card, or Subscriber Identity Module, serves a critical role in mobile devices, specifically in GSM (Global System for Mobile Communications) networks. Its primary purpose is to identify the device on the network. The SIM card contains unique information such as the International Mobile Subscriber Identity (IMSI), which allows the carrier's network to recognize and authenticate the subscriber. This authentication is necessary for the mobile device to connect and communicate over the network, enabling voice calls, text messaging, and mobile data services.

The other options do not align with the primary function of a SIM card. Capturing audio pertains to the device's microphone capabilities, enhancing video quality relates to the device's display and processing capabilities, and connecting to Wi-Fi networks is managed by a different set of hardware and software components, not the SIM card. Thus, the identification and authentication function of the SIM card is essential for enabling mobile connectivity and services in GSM networks.