What is meant by penetration effect of the electrons?

Hi,

Penetration Power means the ability of an orbital to attract an electron. This process is accompanied with release of energy. The Penetration effect of s orbital is the maximum because of the closeness to the nucleus than are the p, d and f orbitals. Thus an s orbital, due it's more penetration effect, releases greater amount of energy than p orbital when it accepts an electron. Similarly the energy released by a d orbital is more than that of a f orbital but less than that of a p orbital .

Hope is clear.

Cheers!