Lanthanoids and the lanthanoid contraction — NEET & JEE Questions

Question 1 · difficulty L1 · recall

What is meant by lanthanoid contraction?

• A. The gradual decrease in atomic and ionic radii across the lanthanoid series with increasing atomic number
• B. The sudden increase in lanthanoid radii after cerium
• C. The decrease in oxidation number from +3 to 0
• D. The conversion of lanthanoids into actinoids

Question 2 · difficulty L2 · understanding

What is the main cause of lanthanoid contraction?

• A. Very effective shielding by 4f electrons
• B. Poor shielding of increasing nuclear charge by 4f electrons
• C. Loss of all 4f electrons across the series
• D. A decrease in nuclear charge from La to Lu

Question 3 · difficulty L2 · understanding

Which oxidation state is most common for lanthanoids?

• A. +1
• B. +2
• C. +3
• D. +6

Question 4 · difficulty L2 · understanding

One important consequence of lanthanoid contraction is the close similarity in size of which pair?

• A. Na and K
• B. Zr and Hf
• C. Cr and Mo
• D. Cu and Ag

Question 5 · difficulty L3 · application

Which trend is expected for the ionic radii of $Ln^{3+}$ ions from La to Lu?

• A. They increase regularly
• B. They decrease gradually
• C. They remain exactly constant
• D. They alternate between large and small values

Question 6 · difficulty L3 · application

How does the basic character of lanthanoid hydroxides $Ln(OH)_3$ generally change from La to Lu?

• A. It increases
• B. It decreases
• C. It remains exactly constant
• D. It first vanishes and then becomes strongly basic

Question 7 · difficulty L3 · application

Why are neighbouring lanthanoids difficult to separate from one another?

• A. They commonly have the same +3 oxidation state and very similar ionic sizes
• B. They all have exactly the same atomic mass
• C. They are all gases at room temperature
• D. They possess identical electronic configurations

Question 8 · difficulty L3 · application

Which statement best explains why Zr and Hf show very similar chemical properties?

• A. They have identical atomic numbers
• B. Lanthanoid contraction makes their atomic and ionic sizes very similar
• C. Hf has no d electrons
• D. Zr belongs to the lanthanoid series

Question 9 · difficulty L4 · application

Consider $La^{3+}$ and $Lu^{3+}$. Which statement is correct?

• A. $Lu^{3+}$ is larger because it has more electrons
• B. $Lu^{3+}$ is smaller because the increase in nuclear charge is poorly shielded by 4f electrons
• C. $La^{3+}$ and $Lu^{3+}$ have identical radii
• D. $La^{3+}$ is smaller because it has fewer protons

Question 10 · difficulty L4 · application

Which pair of observations is correctly explained by lanthanoid contraction?

• A. Gradual decrease in $Ln^{3+}$ radius and similarity of Zr and Hf
• B. Increase in $Ln^{3+}$ radius and strong difference between Zr and Hf
• C. Constant lanthanoid radius and disappearance of the +3 oxidation state
• D. Decrease in nuclear charge and increase in hydroxide basicity from La to Lu