Regarding Application of UNO Board

What will happen when i ON continuously My UNO Board 24X7..???

I think you meant what can happen if you left your arduino open 24/7 well i never tried but i saw a lot of people doing it without any difficulties so i think it should be fine

It will run your code 24/7 if the power remains in spec. I have an Uno that has run 24/7 for over a year with no problems.