(1) He expressed a hope that you would soon be well again.
In the sentence (1), "that" is correct, and "that you would soon be well again" is a noun clause in apposition.
(2) This problem leads to fierce rivalry in which/that an employee must compete with 50 others. But in the sentence (2), "in which" is better. Even some English people say that "in that" is also correct. But I don't know why?
Question 1. Can you explain to me when to use "preposition + which" (adjective clause) or "that clause" (noun clause in apposition)
Question 2. What is the difference between "in which" and "in that" in the sentence (2)
I hope to receive your advice. Many thanks in advance.