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

Answer 1

c) for transition elements, the 3d-orbitals are filled with  electrons after 3p-orbitals and before 4s-orbitals is incorrect .

Explanation:

The d− sub shells are not filled with electrons monotonically with increase in atomic number. There are some exceptions lik Cr,Cu etc.

for example .

cr electronic configuration is : [Ar] 3d⁵ 4s¹

in cu and cr the 4s1 is filled prior to d subshell .