Can I give my rat Children's Advil for a broken or twisted ankle?

Hello there! This does sound like a reasonable dose that's on the high end of the recommended range, however, there are better pain reliever choices available through your veterinarian that run less risk of gastrointestinal bleeding in rats than ibuprofen does. While this is unlikely to occur with one dose at this amount, the longer it's used, the more GI irritation will occur. I strongly suggest bringing Liquor to the vet for evaluation of his twisted or broken ankle as soon as possible, especially if he is non-weight bearing (not putting any pressure on it at all) or if the area appears swollen. It looks like there's a vet near you that sees exotics:
Links Road Animal and Bird Clinic
41 The Links Rd, North York, ON M2P 1T7, Canada
+1 416-223-1165

At the vet's office, he'll get a full physical exam, and they may recommend an x-ray to detect any fractures. In the meantime, try to keep Liquor confined to a small space, and make sure his food and water are easily accessible. The more rest he gets, the better he'll heal. Good luck, and I hope that Liquor feels better soon!