I have just ordered MFRC 522 RFID reader from amzon, and I have also orders 5 RFID tags with keychains and a arduino uno board for my project, I have received RFID reader and tags and I have tested the tags with my Sony xperia NFC. The tags that I received with the readers are working fine but the key chain ones are not working. I think because of the frequency difference 13.56 MHz and 125 KHz. So, please tell will this key chain tags work with the Reader
You are correct NFC is 13.56MHz the key chain ones you are referring to are most likely 125kHz The reader you have will only read 13.56MHz this is the NFC and HID cards. If you want to read the Key Chain ones you will need a reader like this one. Weigand 26 Card Reader Most Phones will not read the 125kHz
You can buy a 125 kHz reader from eBay for around $7. I got one like this:
You can communicate with it (listen to it) with a single serial pin (plus ground and power of course). I have a post about that board which describes the connections.
So, please tell will this key chain tags work with the Reader
No, the 125 kHz tags won't work with the 13.56 MHz reader. However you can work around this (if you want to) by using the 125 kHz tags with a different reader.