When did the supercontinent pangaea start to break up?

The correct answer is - 175 million years ago.

Pangaea was a supercontinent which was consisted of all the continental masses we know nowadays, just they were all merged into one very large land mass. This supercontinent started to form from the land masses that existed prior to it, and because of the tectonic activity they merged roughly around 335 million years ago. The continent existed during the Paleozoic era, as well as the early Mesozoic era.

With the breaking up of this continent because of the tectonic activity, it split initially into two large continents, Laurasia on the north, and Gondwanaland on the south. With the later break up, Laurasia split into Eurasia and North America, while Gondwanaland split into South America, India (which later moved towards Eurasia and merged with it), Antarctica, and Australia. The formation of the modern day continents also resulted in the formation of multiple oceans instead of one.