Which electron is, on average, closer to the nucleus: an electron in a 2s orbital or an electron in a 3s orbital?
In order to answer this question, we need to be clear about the concept of ‘penetration of the orbitals towards the nucleus.
Penetration describes the proximity to which an electron can approach to the nucleus.
And for different values of shell (n) and sub shell (l), penetrating power of an electron follows this trend:
Orbitals which are close to nucleus experience greater attraction and have lesser energy.