d and f BLOCK ELEMENTS

What is the main reason Ce⁴⁺ is considered a good analytical reagent despite being a strong oxidant?

• The reaction rate for oxidizing water is very slow
• It is easily reduced back to Ce³⁺
• It is non-toxic
• It is inexpensive

Which statement best describes the atomic radii trend across the Lanthanoid series compared to the ionic radii trend of M³⁺ ions?

• The decrease in atomic radii is less regular than the decrease in M³⁺ ionic radii
• The decrease in atomic radii is more regular than the decrease in M³⁺ ionic radii
• Both atomic and ionic radii decrease regularly
• Atomic radii remain constant while ionic radii decrease

How does the shielding effect between 4f electrons compare to that between d electrons?

• Shielding between 4f electrons is less effective than between d electrons
• Shielding between 4f electrons is more effective than between d electrons
• Shielding between 4f electrons is equal to that between d electrons
• 4f electrons provide perfect shielding

What is the primary reason for the occasional formation of +2 and +4 ions by Lanthanoids, despite +3 being predominant?

• Extra stability from empty, half-filled, or filled f subshells
• Lower ionization energies overall
• Higher electronegativity
• Greater atomic size

In which type of compounds do Pr, Nd, Tb, and Dy exhibit the +4 oxidation state?

• Only in oxides (MO₂)
• In aqueous solutions
• In halides
• In sulfides