My friend wanna have a try of pokemon r/b

but he uses a illegal emulator

i wanna know if it can be legal

if not, he need a android gb emulator and a rom so im looking for it now

The best option on Android is the latest release of GSE (currently v0.3) https://github.com/CasualPokePlayer/GSE/releases/tag/v0.3 on GBP mode, with a GBC bios image. If GSE does not work on the device, then the relatively new mobile GB/GBC emulator t3boy https://t3boy.vercel.app/ with a GBC bios image is accurate and allowed on the leaderboard currently for a trial period.

You will need to get the GBC bios and the game itself on your own. We are not allowed to provide any help regarding this.