This chapter is crucial because it explains how inner transition elements (3d, 4f, 5f) differ in electronic structure, magnetism, crystal-field splitting, oxidation states, and chemical reactivity. Board and competitive exams frequently test core ideas like high-spin vs low-spin complexes, CFSE/Jahn–Teller distortions, lanthanoid contraction, and redox behavior of f-block elements—often directly using standard numerical values and Hund’s rule.
25
Minutes
20
Questions
1 / -0
Marking
Q1. Calculate the spin-only magnetic moment (in Bohr magneton, BM) of the octahedral complex . Assume is a weak-field ligand and use the spin-only formula , where is the number of unpaired electrons.
Q2. For the octahedral complexes and (metal ion , ), predict which complex is paramagnetic and state the spin-only magnetic moment (in BM) of the paramagnetic one. Assume is a weak-field ligand and is a strong-field ligand.
paramagnetic with ; paramagnetic with
paramagnetic with ; diamagnetic
Both and are diamagnetic
is paramagnetic (high-spin ) with ; is diamagnetic (low-spin )
Q3. For high-spin octahedral complexes of the 3d metal ions , , and , using the CFSE expression (neglect pairing-energy differences), which ion's complex has the largest stabilization (most negative CFSE)?
Q4. Which of the following statements about Jahn–Teller distortion in the octahedral complexes and is correct? ( is , is .)
Both () and () undergo Jahn–Teller distortion; axial bonds are elongated in both.
() undergoes a strong Jahn–Teller distortion with axial elongation (longer axial Cu–O bonds); () remains essentially regular octahedral.
Only () undergoes Jahn–Teller distortion (axial compression); is regular octahedral.
Neither complex shows any measurable Jahn–Teller effect; both are perfectly octahedral.
Q5. Predict the geometry and magnetic behaviour (number of unpaired electrons) of and (Ni, ).
tetrahedral, paramagnetic (2 unpaired); tetrahedral, paramagnetic (2 unpaired)
Both and are square planar and diamagnetic
square planar and diamagnetic (0 unpaired) due to strong-field CN; tetrahedral and paramagnetic (2 unpaired) due to weak-field Cl
square planar and diamagnetic (0 unpaired) due to strong-field CN; tetrahedral and diamagnetic (0 unpaired)
Q6. The spin-only magnetic moment (in Bohr magneton, BM) of the complex is:
2.83 BM
3.87 BM
4.90 BM
0 BM
Q7. Both and contain Co in the +3 oxidation state (d). Which complex will have the lower spin-only magnetic moment?
Both complexes will have the same spin-only magnetic moment
Cannot be predicted without numerical values
Q8. Two octahedral complexes of Cr(II) (d) are formed: L1 gives a low-spin d configuration (strong-field, ) and L2 gives a high-spin d configuration (weak-field, ). Using and pairing energy per electron pair, if , which complex is more easily oxidised to Cr(III) (d)?
L1 (low-spin complex)
Both L1 and L2 are equally prone to oxidation
Neither complex is favourably oxidised under these conditions
L2 (high-spin complex)
Q9. Which of the following lanthanoid oxides is expected to be the most basic (i.e., react most readily with water to give the hydroxide)? Consider lanthanide contraction and ionic character of the oxide.
EuO
LaO
LuO
All three oxides have comparable basicity
Q10. Among the trivalent ions Ce, Eu, Gd and Yb, which ion has the largest paramagnetic moment based on Hund’s rule and the spin-only formula (where is the number of unpaired electrons)?
Gd
Eu
Ce
Yb
Q11. Using the spin-only formula (where is the number of unpaired electrons), calculate the spin-only magnetic moment (in Bohr magneton, BM) for the high-spin octahedral ion with electronic configuration .
Q12. Assume is a strong-field ligand (low-spin) and is a weak-field ligand (high-spin). For and (both contain , ), use to estimate the ratio . Which is closest to the correct value?
Q13. Calculate the crystal field stabilization energy (CFSE) in terms of (ignore pairing energy) for (Cr, ) and (Co, , high-spin). Which complex has the greater CFSE and by how much?
; greater by
; greater by
Both have equal CFSE
; greater by
Q14. For the redox couple , the standard potential is . Ligand forms 1:1 complexes with formation constants for and for . At the standard potential for the couple is approximately (use for per electron):
Q15. Assertion (A): The ionic radii and most chemical properties of and are nearly identical.
Reason (R): The lanthanide contraction, arising because electrons poorly shield the increasing nuclear charge, reduces the expected increase in size across the lanthanide series and makes elements like comparable in size to corresponding elements like .
Choose the correct option.
Both A and R are true, and R correctly explains A.
Both A and R are true, but R does not explain A.
A is true but R is false.
A is false but R is true.
...and 5 more challenging questions available in the interactive simulator.