The principal quantum number is a number which determines the main energy level or principal shell to which the electron of the atom belongs. It also gives the average distance of the electron from the nucleus and also specifies the energy value of the electron.

Azimuthal quantum number is the figure which determines the sub shell in a principal shell to which an electron belongs and it also signifies the number of subshell present in the principal shell.

In the periodic table, a period indicates the value of the principal quantum number [n] denotes the total number of shells present in the atom of the element. Each period starts with the filling of principal quantum number [n]. The value of principal quantum number for the sixth period is 6. For n = 6, azimuthal quantum number [L] can have values of 0, 1,2,3,4. According to Aufbau’s principle, electrons are added to different orbitals in order of their increasing energies. Thus, the 6d shell has a greater energy as compared to the 7s subshell.

In the 6^th period, electrons can be filled in only 6s, 4f, 5d, and 6 p subshells. So, the 6s subshell consists of 1 orbital, 4f subshell consists of 7 orbitals, 5d subshell has 5 orbitals and 6p subshell has three orbitals. As a result, the total number of orbitals present is 16. According to Pauli’s exclusion principle, only 2 electrons can be accommodated in each orbital. So, 32 electrons can be accommodated at a maximum level in 16 orbitals.

Therefore 32 elements would be present in the 6^th period of the periodic table.