Hi Abhinav(virus), quite the username you've got there! Rooting is easy and I'll assume you know the risks involved already. You can get the required A21 drivers and root tool from plenty of reputable places like XDA Developers.
Once you have the drivers and tool downloaded on your PC, just open the zip file, save the driver and tool to your desktop. Connect your phone to your PC and install the drivers, then you're ready to root your KarbonnA21! You may need to temporarily turn off your antivirus if you get a ''blocked'' pop up. Open the root tool you downloaded, click ''root'' (ignore it if it says your device is already rooted) and sit back and wait. That's it. Your phone will reboot and voila, it will be rooted.
You can confirm you have root access and then start flashing whatever custom ROMs you like. Please read about the risks involved if you are not already aware, and make sure you are comfortable with the possibility of bricking your phone as AndroidPIT cannot take any responsibility if it all goes bad. Good luck and enjoy your rooted device!
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