Vostro 3450 is not on Google's Certified models list for ChromeOS Flex. However, you could still try it and it may work. Be certain that you understand the limitations of Flex, as it will not allow some of your hardware to function.  As an alternative, you could install a Linux OS made for weaker systems, such as Xubuntu or Lubuntu or Puppy. You could also try Ubuntu, though it may not run as efficiently as the others that I mentioned. If you have 8 GB of RAM and are running a licensed Windows 7, 8 or 8.1, you could do the free upgrade to Windows 10. I use Windows 10 on laptops as old as yours.
I just want to ask as I want to make my pc new
Does Vostro 3450 supports chrome os flex