Six deceptive problems that no one can solve

This is the title of the article which appeared here 

The problems are
1. Twin Prime Conjecture
2. The Moving Sofa Problem
3. The Collatz Conjecture
4. The Beal Conjecture
5. The Inscribed Square Problem
6. Goldbach Conjecture

I am aware of the problems number 1,3 and 6. So I need to investigate the other 3. Which are Moving Sofa, Beal Conjecture and the Inscribed Square Problem.