Student or Learner
I'm wondering if the following four sentences are natural?
The country is the most rainy one in the world.
The country is the rainiest one in the world.
The country is the wettest one in the world.
The country has the highest rainfall in the world.
You don't need "one" in any of them. The most natural of the four, in my opinion, is the last.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.