ChromeBook And Ubuntu
 

I Just Wanted To Ask That Can We Replace Chrome OS With Ubuntu On Chromebook

Oftentimes, yes. Not always. We'd need to know the model of chromebook to know for sure, but if it's an x86-based chromebook, then most likely you can.

Xolo Chromebook (HR-116R)
i dont have it but i am thinking about it
but i dont think chrome os is good enough like ubuntu or other linux os's
but as i have heard linux can run on any system thats why i was asking

The answer is a solid maybe, but not without a LOT of work, and probably a lot of difficulty. That Chromebook is ARM based, not x86 based, so doesn't use a normal BIOS that can be flashed. It uses a bootloader more like an android phone, and so it's not as easy to modify it to install a different OS. And even once you've figured out HOW to install linux on there, and how you're going to mange booting after installing it, you'd still be extremely limited in what distro's you could run. However, Ubuntu does have a version that supports ARM officially, so it MIGHT work.

ARM chromebooks can run Linux, but not all Linux distros have ARM versions available. Debian can run on any chromebook, through various methods. The easiest is to use the crouton scripts to run it (or Ubuntu for that matter) in a chroot. If you want, you can flash SeaBIOS through any of several methods to completely remove ChromeOS and replace it with the distro of your choice. Chromebooks are not at all unique, they're just standard laptops, but they use UEFI not grub. You have to know how to get around the UEFI lockdown, and that's not rocket science. If you want to run Linux from an external drive, all you need to do is enable developer mode and set some flags. None of this is remotely like Android phones.

that means can i do it with Arch Linux ARM,Ubuntu ARM,Debian ARM,Fedora ARM

Correct.