How many episodes of mass extinction of species have occurred in the history of life on Earth before humans appeared on the scene?

Five

The answer is (c) Five.

The passage mentions that during the long period (> 3 billion years) since the origin and diversification of life on Earth, there were five episodes of mass extinction of species before humans appeared on the scene.

 These are:(For extra knowledge out of ncert)

1. The Ordovician-Silurian extinction event, which occurred about 440 million years ago. This event wiped out about 85% of all marine species.
2. The Late Devonian extinction event, which occurred about 375 million years ago. This event wiped out about 70% of all marine species.
3. The Permian-Triassic extinction event, which occurred about 252 million years ago. This event is the most severe mass extinction in Earth's history, and it wiped out about 96% of all marine species and 70% of all terrestrial vertebrate species.
4. The Triassic-Jurassic extinction event, which occurred about 201 million years ago. This event wiped out about 20% of all marine species.
5. The Cretaceous-Paleogene extinction event, which occurred about 66 million years ago. This event is commonly known as the "K-T extinction event," and it is thought to have been caused by the impact of an asteroid or comet. This event wiped out about 75% of all marine species and 76% of all terrestrial vertebrate species, including the dinosaurs.

It is important to note that these are just the major episodes of mass extinction. There have been many other smaller extinction events throughout Earth's history.