Question

Lanthanides are.
A) 15 elements in the seventh period \[\left( \text{At.no.90 to 103} \right)\] that are filling $5f$ sublevel.
B) 15 elements in the sixth period $\left( \text{At.no.57 to 71} \right)$ that are filling $4f$ and $5d$ sublevel.
C) 15 elements in the seventh period $\left( \text{At.no.57 to 71} \right)$ that are filling $4f$ and $5d$ sublevel
D) 15 elements in the sixth period \[\left( \text{At.no.90 to 103} \right)\]

Answer 1

Hint: We know that Lanthanoids, likewise called lanthanides are 15 sequential compound components in the intermittent table from lanthanum to lutetium (nuclear numbers $57 - 71$). With scandium and yttrium, they make up the uncommon earth metals. Their molecules have comparable arrangements and comparable physical and compound conduct; the most well-known valencies are 3.

Complete step by step answer:
We must remember that the lanthanide or lanthanoid arrangement of components contains the fifteen metallic substance components with nuclear numbers $57$ through $71$, from Lanthanum through Lutetium.
We have to remember that the key attributes and properties of lanthanide which are listed below as,
They have radiance and are brilliant in appearance.
They are delicate metals and can even be cut with a blade
The components have distinctive response propensities relying upon basicity. Some are receptive while some set aside some effort to respond.
Lanthanides can erode or get weak on the off chance that they are sullied with different metals or non-metals.
They all generally structure a trivalent compound. Here and there they can likewise shape divalent or trivalent mixes.
We have to know that the lanthanum is utilized all in all conversations of lanthanide science to allude to any lanthanide. Everything except one of the lanthanides are f-block components, compared to the filling of the 4f electron shell; Lutetium, a d-block component, is additionally commonly viewed as a lanthanide because of its synthetic likenesses with the other fourteen.
Therefore, the option (B) is correct.

Note: We have to know that the nuclear size or the ionic radii of tri positive lanthanide particles decline consistently from La to Lu because of expanding atomic charge and electrons entering internal \[\left( {n - 2} \right)f\] orbital. This continuous diminishing in the size with an expanding nuclear number is called lanthanide contraction.