Distinguish between shell and subshell.

Hint :As we know an atom is known to be a basic unit of matter which is composed of many subatomic particles like protons, neutrons and electrons. Nucleus of an atom is made up of protons and neutrons together while electrons in an atom tend to revolve around the atoms in a particular path.
Pathway of any electron around the nucleus is determined in terms of orbits, orbitals, shells and subshells.

Complete Step By Step Answer:
Schrodinger wave equation led to the concept of most probable regions in the place of well-defined circular paths as orbitals, which are later defined as “orbital is a region in a space around the nucleus of an atom where the probability of finding an electron is supposed to be maximum”.
In order to describe each electron in different orbitals, we need to use a set of principal quantum numbers.
Principal quantum number designated by $ \left( n \right) $ is defined as the quantum number which helps in determining the main shell or level in which probability of finding the electron is maximum.
Value of the shell is always a whole number starting from 1.

As the value of principal quantum number increases the average distance between the nucleus and electron present in a particular shell increases.
Subshell of any particular electron in a shell is well described by the Azimuthal quantum number $ \left( l \right) $ .
This quantum number helps in determining the angular momentum of an electron in its particular subshell.
Various subshells of electrons are also represented as alphabets.

Value of the subshell cannot be a negative integer and it ranges from $ \left( {n - 1} \right) $ , where $ n $ is the principal quantum number.
For example – for any electron present in shell $ \left( {n = 2} \right) $ , the value of its subshells is $ \left( {l = 0,1} \right) $ .
Finally we conclude that $ \left( n \right) $ describes the shell, which helps to determine the size of the orbital, the energy of the orbital and average distance between the nucleus and electron.
While $ \left( l \right) $ determine the subshell and shape of the orbital, to some extent it also helps in determining the energy of the orbital in a multi-electron atom.

Note :
Magnetic quantum number $ \left( {{m_l}} \right) $ is used to relate a subshell of an electron with its orbitals. This quantum number is used to describe the magnetic behavior of electrons which tend to orient themselves in a particular region around the nucleus known as orbitals.
Do not confuse orbital with orbit which is a well defined circular path of electrons around the nucleus.