RFID Reader MFRC522 Module uses NXP front end chip. Its working frequency is 13.56MHz ,That means RFID Reader MFRC522 used 13.56 Mhz rfid antenna. This RFID Reader MFRC522 module comes with inbuilt PCB trace antenna for more stable oparation. This RFID reader module comes with matching MIFAIR key chain and RFID card.
So in short An RFID tag (sometimes called an RFID transponder ) consists of a chip , some memory and an antenna.
Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects short-range Rfid tags . This module communicates over UART or I2C with simple protocols. This module can use as MIFARE RC522 arduino module.