Why does an electron enter 4s orbital but not 3d after completely filling 3p orbital?

The electron enters into 4 s orbital after filling 3 p orbital but not into 3d . Explain the reason .

According to Aufbau principle, electron enter first into which of the following orbital ?

The order of filling of electrons in the orbital of an atom will be

Number of nodes in 3p orbital is

Number of nodes in 3p orbital is

The bromine atom possesses 35 electrons. It contains 6 electrons in 2p orbital, 6 electrons in 3p orbital and 5 electrons in 4p orbital. Which of these electrons experience the lowest effective nuclear charge ?

Electron in _______orbit does not radiate energy.

For carbon (C) atom (Z=6), where does the 6th electron go? Whether the electron pairs up in the same p-orbital or will it go to the next p-orbital?

Copper is regarded as transition metal, though it has completely filled 3d-orbitals. Explain.

(A): Electron gain enthalpy of noble gases is very less (R): Atoms of noble gases have completely filled orbitals