The Fundamental Theorem of Arithmetic is the easiest of the 3, but it isn't as fundamental as you think it is. It states that every number can be prime factorized uniquely as a product of primes. No 2 numbers have the same prime factorization, and no number has 2 distinct prime factorizations.
For instance, \(10=2\times5\).
\(10\) cannot be represented as another distinct prime factorizations and no other number is prime factorized into \(2\times5\).
You are welcome to prove it in the comments below.