Question

The period number in the long form of the periodic table is equal to
(a) magnetic quantum number of any element of the period
(b) the atomic number of any element of the period
(c) Maximum principal quantum number of any element of the period
(d) maximum azimuthal quantum number of any element of the period

Answer 1

Answer: (c) Maximum principal quantum number of any element of the period

Since each period starts with the filling of electrons in a new principal quantum number, therefore, the period number in the long form of the periodic table refers to the maximum principal quantum number of any element in the period.

Period number = maximum n of any element (where, n = principal quantum number).