Question

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 ionization enthalpies of elements generally increase with increase in atomic number as we go along a period.

Answer 1

Answer: (C)

According to Aufbau principle, "in the ground state of the atoms, the orbitals are filled in order of their increasing energies." The increasing order of energy according to (n + I) rule is : 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s ... etc.
Therefore, the 3d orbitals are filled with electrons after 4s orbitals and before 4p orbitals.