Check your About This Mac from the black Apple icon in the upper left hand corner. Select Overview and go down to Network/WiFi.
This is what my Mac Mini supports:
Interfaces:
en1:
Card Type: AirPort Extreme (0x14E4, 0x10E)
Firmware Version: Broadcom BCM43xx 1.0 (7.15.124.12.10)
MAC Address:
Locale: FCC
Country Code: X0
Supported PHY Modes: 802.11 a/b/g/nI don't think AC mode is supported.
