Coordination compounds form the foundation of modern inorganic chemistry and appear frequently in CBSE boards as well as competitive exams like JEE/NEET. Mastery of concepts such as oxidation state, stereochemistry of coordination complexes, spin states (high-spin/low-spin), magnetic properties, and Jahn–Teller effects is essential because questions often combine multiple ideas in one problem and require careful application of rules.
20
Minutes
15
Questions
1 / -0
Marking
Q1. (An octahedral complex of shows a magnetic moment of at room temperature. Using the spin-only formula , determine the number of unpaired electrons and whether the complex is high-spin or low-spin.)
(Three unpaired electrons; high-spin)
(Four unpaired electrons; high-spin)
(Five unpaired electrons; high-spin)
(One unpaired electron; low-spin)
Q2. (For the octahedral complex (en = ethylenediamine, bidentate), how many stereoisomers (geometrical + optical) are possible and how many of them are optically active?)
(Three stereoisomers in total; two are optically active (a cis enantiomeric pair) and one (trans) is achiral)
(Two stereoisomers in total; neither is optically active)
(Four stereoisomers in total; all four are optically active)
(One stereoisomer only; it is optically active)
Q3. (For an octahedral metal ion the pairing energy is . Ligand gives while ligand gives . Predict the most likely spin states for and , respectively.)
(Both and will be low-spin)
(Both and will be high-spin)
( high-spin; low-spin)
( low-spin; high-spin)
Q4. (When excess is added to an aqueous solution of , the major isolated product is . Which of the following explanations best accounts for formation of the trans product?)
(The trans isomer uniquely maximizes crystal-field stabilization energy for Pt(II), so it is thermodynamically preferred)
( has a stronger trans-effect than or ; after the first substitution the ligand trans to the incoming is labilized, promoting sequential replacement that yields the trans product)
(A Jahn–Teller distortion in the cis isomer forces rearrangement to the trans form)
(Steric repulsion between small ligands forces to bind trans to , directing formation of the trans isomer)
Q5. (Arrange the octahedral aqua complexes in order of decreasing expected Jahn–Teller distortion intensity: (), (, high-spin), (, high-spin), ().)
()
()
()
()
Q6. For the high-spin complex , calculate the spin-only magnetic moment in Bohr magneton. Use , where is the number of unpaired electrons.
Q7. Consider the octahedral complex ion (en = ethylenediamine, bidentate). How many stereoisomers are possible for this complex and how many of them are optically active?
Three stereoisomers; two optically active
Two stereoisomers; both optically active
Three stereoisomers; none optically active
Four stereoisomers; two optically active
Q8. A metal ion in an octahedral field has pairing energy and octahedral splitting . Determine whether the complex will be high-spin or low-spin and calculate its crystal field stabilization energy (CFSE) in kJ·mol (use CFSE for low-spin and for high-spin ).
High-spin; CFSE =
Low-spin; CFSE =
High-spin; CFSE =
Low-spin; CFSE =
Q9. Assertion (A): Octahedral Cu(II) complexes () commonly undergo Jahn–Teller distortion that results in elongation of two axial bonds.
Reason (R): In a octahedral configuration the orbitals () are unevenly occupied, creating electronic degeneracy which is relieved by axial elongation.
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
Q10. Which one of the following complexes will exhibit optical isomerism (enantiomers) but will not display any geometrical (cis–trans) isomerism?
Q11. For the complex , what is the oxidation state of cobalt and the number of -electrons on the metal?
Oxidation state ,
Oxidation state ,
Oxidation state ,
Oxidation state ,
Q12. Which of the following compounds will give a precipitate on addition of due to the presence of free chloride ions in solution?
Q13. Consider and (both contain , ). Which of the following statements is correct regarding their magnetic moments and crystal field stabilization energy (CFSE)?
has a lower magnetic moment and a larger (more negative) CFSE than
has a higher magnetic moment and a larger CFSE than
Both complexes have the same magnetic moment but different CFSE values
has a lower magnetic moment but a smaller (less negative) CFSE than
Q14. Assertion (A): Square‑planar complexes are paramagnetic.
Reason (R): In square‑planar geometry the ligand field splitting is large and arranges the ‑levels so that the lower orbitals can accommodate paired electrons, favouring diamagnetism.
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.
Q15. Metal forms successive complexes with ligand with stepwise formation constants and . If total metal and free ligand concentration (large excess), the fraction of metal present as at equilibrium is approximately: