In what kind of reaction does a single compound produce two or more simpler substances

if two electrons have the same n, the same ℓ, and the same ml, then they are in the same orbital. the pauli exclusion principle states that no two identical fermions (a fancy word for electrons and other subatomic particles like electrons) may occupy the same quantum state in an atom simultaneously.

it's c. elements are placed in rows based on how may valencies electrons have.