realise和realize有什么区别？

没区别，一个是美式英语，一个是英式英语

There is no rule.
没有规则可言。都正确
I was taught to spell realize with a "z" in an American school
美国用realize
I was taught to spell realize with a "s" in an English school
英国用realise

很多动词在英式英语中既可以用-ize结尾，也可以用-ise，美语中一律用-ize结尾。
但有些单词，因为词源的原因，总用-ise结尾,如exercise,advise等。