The period number in the long form
Question:

The period number in the long form of the periodic table is equal to

(i) magnetic quantum number of any element of the period.

(ii) an atomic number of any element of the period.

(iii) maximum Principal quantum number of any element of the period.

(iv) maximum Azimuthal quantum number of any element of the period.

Solution:

Option (iii) maximum Principal quantum number of any element of the period is the answer.