The statement that is not correct for periodic classification of element isA)The properties of elements are periodic function of their atomic numbers B)Non-metallic elements are less in number than metallic elements C)For transition elements, the 3d-orbitals are filled with electron after 3p-orbitals and before 4s-orbitals D)The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period

Options

A. The properties of element are periodic function of their atomic numbers.
B. Non metallic elements are less in number than metallic elements
C. For transition elements the 3d-orbitals are filled with electrons after 3p- orbitals and before 4s-orbitals
D. The first ionisation enthalpies of elements generally increases with increase in atomic number as we go along a period.

Answer

C

Explanation

According to aufbau principle energies of the various orbitals increase in the order `: 1s^(2) ,2 s^(2) 2p, 3s,3p ,4s 3d, 4p……`etc . Therefore 3d- electrons are filled after 4s- and before 4p-orbitals. Thus option ( c) is not correct.