question_answer 1)

  The statement that is not correct for periodic classification of elements is : (a) 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 electrons 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.

Answer:

  (c) For transition elements, the 3J-orbitals are filled with electrons after 3p and 4s-orbitals and before 4p-orbitals. The order of filling the orbitals is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s....