Hi Prahad
I think you can do it cheaper and much more simple:
just connect a capacitor a resitior and a led in series between the connections of the main supply. The led should gave a small signal diode antiparallel. The light of the led is now proportional to the mains voltage.
Tape the led together with an LDR
Use the LDR as the bottom resitor in a voltage divider.
Connect the divider to your stabalized 5V powersupply and the top of the LDR to your ADC.
Thats all !!!
I've done it several times, it works fine and is completely seperated from mains (galvanic) by the selfbuild optocoupler. In high security applications you can increase the creeping distance by placing a tiny peace of transparant plastic between the led and the LDR.

Best regards

Robert Dugour