The 3s and 3p orbitals have identical energies in the hydrogen atom, but in chlorine atom their energies are much different. Explain.

@ ajanta 
frst of all , hydrogen have 1 electron only , so, its very small compared to chlorine , and being a monoelectronic species , if that electron will get energy somewhere to exicte to any other orbitals , then that will not count at all , and approximate as very small , 
so, they both orbitals are said to be degenerate , 
while in the case of chlorine they have large no of electrons and being electronegativity , it have a much diffrence in energy level when half of the electron will migrate to anathor orbital or excite to anathor orbitals , 
HOPE IT CLEARS NOW