Which of the following can be used by a mobile device to access a secure...

The correct answer is B. Near-field communication (NFC).

According to the CompTIA A+ Core 1 220-1201 objectives under Mobile Devices and Security:

NFC is commonly used for secure access control. Many organizations implement NFC-enabled ID badges or mobile devices to unlock doors, gates, or secure areas.

The mobile device communicates over a very short range (a few centimeters) with a reader to authenticate the user.

Why the other options are incorrect:

A. Hotspot: Provides internet access, not physical building access.

C. Infrared scanner: While used in some legacy devices, it is not commonly implemented for secure mobile access.

D. Geolocation: Can provide location awareness but does not grant direct access to secure physical spaces.