Quantum nos.

don't u thnk u shuld read these frm NCERT or some theory book, becoz explaining here is just like killing time as we have to type too much of theory ............
its better if u get it from a book . WHY WASTE TIME .
Please look into this topic in NCERT..........[1]

Theory Behind The Microscopic Madness -:

SHELL - This is the main energy level in which an electron resides. It is given by the principal quantum number, which is denoted by "n". n can have positive integral(quantized) values starting from 1.
For n = 1,2,3,4 we designate the shells by the names K,L,M,N and so on.

SUBSHELL - This is the sub-energy level in which the electron resides. It is given by the azimuthal quantum number, denoted by "l". "l" satisfies the inequality
0 ≤ l ≤ n -1
for a given value of n.
For n = 1, l = 0, meaning there is only one value of l for the first shell. Hence there is only one subshell possible.
For n = 2, l = 0,1, meaning there are two subshells possible and so on.
l = 0,1,2,3 are designated as s,p,d,f subshells respectively.

ORBITAL - This is the orientation a subshell takes up in presence of an external magnetic field. It is given by the magnetic quantum number "m". m varies as
-l ≤ m ≤ l
including "0".
For l = 0, there is only one orientation or orbital possible(explains why the s-subshell is only spherical).
For l = 1, there are 3 orientations or 3 orbitals
When l = 1, m = 1 indicates the p_x orbital, m = -1 indicates the p_y orbital and m = 0 indicates the p_z orbital.
Similarly you have designations for the d-subshell's orbitals.

SPIN NUMBER - These values indicate NOT the "clockwise" or "counterclockwise" spin as normal theory suggests, but it is a function of the intrinsic angular momentum of the electron. I don't want to confuse you, so you have to just accept your NCERT/pradeep theory. Thing is, you can't tell whether an electron spins clockwise or counterclockwise. If you could, you would be violating Heisenberg's uncertainty principle.
Spin quantum number is +1/2 or -1/2 for fermions like the electron.

If atleast 3 quantum numbers are the same, the fourth shall have to be different.

Thank you very much,Pritish bhaiya.

take my advice if u wanna know more but don't wanna see it frm the book.........
search for the topic in wikipedia..........
i guess Pritish had got this information from wikipedia.........
otherwise no one can type this long reply in few minutes

OK [1]

Sorry to disappoint you Manmay, but none of this is from Wiki. It's from my notes copy. :)
(Except the spin number part about intrinsic angular momentum..I read it a long time ago on Wiki, still remember!)

but i had not told just to see WIKI.........
i asked to see NCERT or other theory books also na