A scientist wants to estimate the mass of an atom. What information can be used to do this?
The masses of the electrons and neutrons can be added together.
The atomic number of the element can be used.
The masses of the protons and neutrons can be added together.
The column number of the periodic table can be used.

The masses of protons and neutrons added together

Explanation:

The neutrons and protons are the only ones that have weight , the electron doesn't ( thats the reason they arent in the middle section )

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.