CBSE Class 12-science Answered

Orbital - The region of space around the nucleus where the possibility of finding an electron is maximum is called an orbital.

Sub shells are a division of main shells (K, L, M, N etc) and are composed of atomic orbitals.Example: s, p, d ,f etc.

Shells represent the Highest level in writing electronic configuration of an atom. It corresponds to the energy level of electron in an atom. It is further divided into subshells. Sub-shell contains orbital.

Example: At the 4^th energy level in electronic configuration, the shell no. is 4, it contains 4 sub-shell s, p, d, f .

Each sub-shell consists of some orbitals where electrons exists (Each orbital can hold up to 2 electrons) 
s sub-shell contain 1 orbital and can hold up to 2 electrons 
p sub shell contain 3 orbitals and can hold up to 6 electrons 
d sub shell contain 5 orbitals and can hold up to 10 electrons 
f sub shell contain 7 orbitals and can hold up to 14 electrons