Hint :Lanthanides are a group of 15 chemical elements whose atomic numbers range from 57 to 71. In the 5d shell, each of these elements has one valence electron. The elements have properties in common with the group's first member, lanthanum. Lanthanides are silver-colored metals that are reactive.
Complete Step By Step Answer:
The lanthanide contraction is described as a greater-than-expected decrease in the ionic radii of the elements in the lanthanide sequence from atomic number 57, lanthanum, to atomic number 71, lutetium, resulting in smaller-than-expected ionic radii for the elements following 72, hafnium. In his series "Geochemische Verteilungsgesetze der Elemente," Norwegian geochemist Victor Goldschmidt coined the expression (Geochemical distribution laws of the elements). The effect is caused by the 4f electrons' ineffective shielding of nuclear charge (nuclear attractive force on electrons); the 6s electrons are attracted towards the nucleus, resulting in a narrower atomic radius.
The average separation of an electron from the nucleus in single-electron atoms is determined by the subshell it belongs to, and it decreases with increasing charge on the nucleus, resulting in a decrease in atomic radius. Increased electrostatic repulsion among electrons partly offsets the decrease in radius caused by an increase in nuclear charge in multi-electron atoms.
The attraction between an electron and the nucleus of any atom of more than one electron is known as the shielding effect, also known as atomic shielding or electron shielding. A change in the attraction forces on the electrons in the atom causes the shielding effect, which is characterised as a reduction in the effective nuclear charge on the electron cloud. It's a kind of electric-field screening that's a little different. This influence is also important in a number of material science programmes.
A "shielding effect" operates in particular: when electrons are applied to outer shells, the outer electrons are shielded from nuclear charge by the electrons already present, resulting in a lower effective charge on the nucleus. The inner electrons' shielding effect diminishes in the order s > p > d > f.
The number of unpaired electrons determines the magnetic moment, and the number of unpaired electrons varies as the structure changes. As a result, the magnetic moment shifts.
Hence option C is correct.
The atomic radius typically decreases as a subshell is filled in a time. The 4f subshell, which is filled over these elements, is not very good at shielding the outer shell (n=5 and n=6) electrons, so this effect is especially pronounced in the case of lanthanides. As a result, the shielding effect is less effective at compensating for the reduction in radius caused by increasing nuclear charge. As a result, "lanthanide contraction" occurs. Lanthanum(III) has an ionic radius of 103 pm, while lutetium has an ionic radius of 86.1 pm (III).