Prioritise. Prioritize. Apologise. Apologize.

Same word, one letter different. People often get confused with the “z” and the “s” in words like these. One way is generally favoured by American English, the other by British English. Which is which?

The answer is slightly complex. The use of ‘z’ was popularised in American English when it was standardised in the 19th Century, whilst ‘s’ has become more widely used in British English, perhaps as a backlash against the American use of ‘z’. However, British spelling has always recognised the use of the suffix ‘ize’, with the Oxford English Dictionary generally favouring it.

There are some American spellings using ‘z’ though that are not acceptable in British English, ‘analyze’ being one.
Most importantly though, it’s best to be consistent. So if you start off by “organizing”, you should continue by “prioritizing”.