Question

Which of the following is true according to the Fajan’s rule?
A. smaller the anion higher is the polarizing power
B. larger the size of the cation had its polarizability
C. cations with pseudo noble gas configuration have relatively higher polarising power than those with noble gas configuration
D. none of these

Answer 1

Hint: The cation having pseudo noble gas configuration will not have eight electrons in its valence shell like a noble gas but its d orbital will be completely filled. A d orbital has the maximum capacity of accommodating 10 electrons.
Polarizing power is associated with the cation which tells its tendency to attract an electron cloud of the anion towards itself.

Complete step by step answer:
Fajan’s rule is used to determine whether a compound is ionic or covalent.
According to this rule, no bond is fully ionic or covalent. A covalent bond has some ionic character and vice versa.
For the cations with the same charge and size, the elements with a pseudo noble gas configuration that is the transition elements with inner orbital configuration, $(n-1){{d}^{n}}n{{s}^{0}}$ have less screening power. So it has less effective nuclear charge and more polarizing power than the cations with $n{{s}^{2}}n{{p}^{6}}$ configuration (noble gas configuration) which are the alkali and the alkaline earth metals.
So, the former shows more covalent character than the latter.
So, the correct option is C.

Note: Other factors on which Fajan’s rule depends are:
Size of the ion – smaller the size of the cation, more the polarizing power, more the covalent character of the ionic bond.
Charge of the ion – greater the charge of the cation, greater the covalent character.