Can we use RFID reader with an arduino to detect a RFID which is 5m away? I mean if there is a possibility? Please help...!!!
Car electronic tolling tags are RFID afaik, and they work over distances of many metres. That's not an Arduino issue as such.
In your case you'll need to investigate such long range readers and see if they communicate in a similar way to the ones usually used with Arduinos, ie just 2 wires over serial. (Or maybe they have some other connection, maybe I2C, but ypu need to start with the reader, not the Arduino end I think.)
"long range rfid" gives almost 1.5M google hits....
Tags capable of being read over that distance are normally different from the normal 125KHz or 13MHz type normally used with the Arduino.
Do you have control over what tags are being used here?