The statement that is not correct for periodic classification of elements is
(a) The properties of elements are the periodic function of their atomic numbers
(b) Non-metallic elements are less in numbers than metallic elements
(c) For transition elements, the 3d orbitals are filled with electrons after 3 p - orbitals and before 4s orbitals
(d) the first ionization enthalpies of elements generally increase with the increase in atomic number as we go along a period
Answer: (c).
In cases of transition elements (or any elements), the order of filling of electrons in the various orbital is 3p < 4s <3d, Thus 3d orbital is filled when 4s orbital gets completely filled (Aufbau Principle).