Scotland the brave is quite a nice tune but not the type you want for a national anthem.
Why not? What sort of tunes do you find appropriate?
A few reasons:
1. Scotland the Brave is fast. Really really fast. It is difficult to fit any words to it and even if you succeed it will be difficult for people to sing them, and national anthems should be fairly easy for even the unmusical to sing.
2. It's very very upbeat. A national anthem should be able to sound solemn.
3. It's basically designed to be played on either the bagpipes or the fiddle, ideally a national anthem would be able to played on most orchestral instruments.
4. The only time I've ever heard anyone play it is at ceilidh's or as something that plays electronically if you push the button of a cuddly bagpipe toy or nessie.