Which of the following condition is suitable for cathode ray discharge tube?

How many electrons can exist with the principal quantum number’s value as 4?

No two electrons have the same set of all four quantum numbers.

Δx. Δp ≥ h/4π.

Neutrally charged particles are protons.

Determining the exact position and velocity of an electron is impossible at a time.

What’s the radius of 1st orbit of He+ atom?

____ frequency, is the minimum frequency required to eject an electron when photons hit the metal surface.