[tkttan]

(Electron in the shells of a lower quantum number have a stronger shielding effect compared to with electrons in the shells of a higher quantum number.)

The above sentence should be corrected to (Electron in the shells of a "higher" quantum number have a stronger shielding effect compared to with electrons in the shells of a "lower" quantum number.)

Am i right?

[kriggy]

Why do you think so?

[tkttan]

Actually, what is quantum number? Can explain it to me?

[Corribus]

Because of quantum confinement effects, electrons and other very light particles can only take on certain values of energy. A corollary to this is that they can only have certain, quantized values of angular momentum and do have not equal probability of existing everywhere in space. The quantized energy and momentum values are represented by quantum numbers, which specify the state of the particle as well as the observable (energy, e.g.) associated with that state.