Let's take a look at the sentences you provided and check their grammar step by step:
- Original: The rainforest is thick, hot and rainy.
- Correction: The rainforest is thick, hot, and rainy.
- Explanation: When listing three or more adjectives, it's correct to put a comma after each adjective except the last one. This comma is called the Oxford comma. So, adding a comma after 'hot' is preferred.
- Original: The Amazon has the largest rainforest in world.
- Correction: The Amazon has the largest rainforest in the world.
- Explanation: We need to include the article 'the' before 'world' because it refers to a specific, known place.
Final corrected sentences:
The rainforest is thick, hot, and rainy.
The Amazon has the largest rainforest in the world.