I found those phrases here. From my understanding these mean:
大きいの = the ones that are big
きれいなの = the one that is pretty | the ones that are pretty
Am I right? I didn't manage to find any explanation online and on my grammar book. Is it correct to use the same construction with other tenses, like 大きくないの (= the one that is not big) or きれいだったの (= the one that was pretty)?