Question

Regarding the magnetic properties of lanthanides and actinides are correct statement is:
A. Lanthanides are weakly paramagnetic while actinides are strongly paramagnetic.
B. Quenching of orbital contribution is greater in lanthanides than in actinides.
C. ${ 5f }$ electrons in actinides are too diffuse and are less effectively shielded which results in considerable quenching of orbital contribution, and hence the magnetic movements of actinides are significantly less than theoretically predicted values.
D. Because of diffused f electrons, there is no quenching of orbital contribution towards the magnetic movement.

Answer 1

Hint: The elements of lanthanide and actinide series are characterized by filling of ${ (n-2) f }$ subshell. They possess almost alike outermost electronic configuration consequently have indistinguishable properties.

Complete step-by-step answer:
Lanthanides: ${ 4f }$ series elements of f-block elements in a periodic table are called lanthanides. This includes cerium (Ce) to lutetium (Lu).
Actinides: ${ 5f }$ series elements of f-block elements in a periodic table are called actinides. This includes thorium (Th) to lawrencium (Lr).
${ 5f }$ electrons in actinides are too dispersed and are less adequately shielded which brings about considerable quenching of orbital contribution, and subsequently, the magnetic movements of actinides are altogether less than theoretically predicted values. Hence, this statement is true.
The lanthanides and actinides are paramagnetic due to the presence of unpaired electrons. Elements of these series have variable oxidation states as they can lose multiple electrons to form a wide range of different ions.
Quenching refers to the sudden and rapid cooling of a hot substance to acquire some properties. Most of the time, quenching either makes a substance more brittle or more strong.
For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and is hence of no allowance.
The correct option is C.

Note: The possibility to make a mistake is that you may choose option A that lanthanides are less paramagnetic as compared to actinides but they show variable oxidation states and most of the compounds of these are paramagnetic.