The Lanthanoids & Actinoids(20 Jan) - Free MCQ Practice Test with solutions,

The actinoids are said to be most radioactive metals because in this group all the metals have very oxidation number and are very rare metals found on earth and it has all the elements radioactive in its group and it has most radioactive metal uranium in it's group.

The correct answer is option A

Misch metal, alloy consisting of about 50 percent cerium, 25 percent lanthanum, 15 percent neodymium, and 10 percent other rare-earth metals.

The correct answer is option A
The most common oxidation state of actinide is +3. It is obtained when one 6d and two 7s electrons are lost. The general electronic configuration of actinides may be written as [Rn]5f¹⁻¹⁴6d⁰⁻¹7s².

The correct answer is option D
Atomic number of Eu is 63 so electronic configuration of Eu is, Eu=[xe] 4f⁹ Hence,Eu⁺³=[xe]4f⁶

The correct answer is option C
Cerium
Electronic configuration of Ce=[Xe]4f¹5d¹6s²
Formation of Ce⁺⁴ is favoured by its noble gas configuration due to which it shows +4 oxidation state.
It can be easily converted into Ce⁺³, due to which Ce⁺⁴ acts as an oxidising agent.

The lanthanide are f-block elements which contain seven f-orbitals . The maximum electrons can be filled in f-orbitals are 14. Hence, lanthanide have total 14 elements.

In +3 oxidation state Lanthanum(La) achieves the noble gas configuration.

The correct answer is option C
The 5f orbitals (in case of actinoids) have a poorer shielding effect than 4f orbitals (in lanthanoids). Thus, the effective nuclear charge experienced by electron in valence shells in case of actinoids is greater than that in lanthaniods.

The correct answer is Option A
Lanthanides show variable oxidation states. The most stable oxidation state of Lanthanides is +3. They also show +2 and +4 oxidation states due to the presence of either half filled or completely filled or empty 4f subshell.

Any atom exhibit oxidation state in which it is found to be stable. It is second element of Lanthanide series having atomic number 58. General electronic configuration is
[Xe] 4f¹ 5d¹ 6s².
Lanthanide are very less electronegative. Their electronegative value is nearly equal to s-block elements. So they can lose electrons to form cation. When Cerium loses 4 e-, it will acquire fully field electronic configuration of Xenon (2,8,18,18,8). As fully filed or half filed electronic configuration possesses extra stability.
Therefore, Cerium exhibits +4 oxidation state.