Crystalline structures of complexes MCQs With Answer

Crystalline structures of complexes MCQs With Answer is a focused guide for B. Pharm students exploring how coordination complexes form ordered solid lattices, influence drug stability, solubility and bioavailability, and are characterized by techniques like X‑ray diffraction and thermal analysis. This introduction covers core concepts — unit cells, crystal systems, coordination geometries, crystal field effects, polymorphism and packing — with practical pharmaceutical relevance such as polymorph screening and hydrate formation. Keywords: crystalline structures, coordination complexes, unit cell, crystal lattice, X‑ray diffraction, polymorphism, B. Pharm, MCQs. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the smallest repeating unit in a crystal that, by translation, recreates the entire lattice?

• Unit cell
• Basis
• Lattice point
• Motif

Correct Answer: Unit cell

Q2. Which description best defines a Bravais lattice?

• A crystal described by its chemical formula
• A set of discrete points repeated periodically in three dimensions
• The arrangement of electrons around a metal center
• A single molecule in a crystal

Correct Answer: A set of discrete points repeated periodically in three dimensions

Q3. Which crystal system has three axes of unequal length and all angles different from 90°?

• Cubic
• Orthorhombic
• Monoclinic
• Triclinic

Correct Answer: Triclinic

Q4. In a face-centered cubic (FCC) unit cell, how many atoms per unit cell are present if atoms are at lattice points?

• 1
• 2
• 4
• 6

Correct Answer: 4

Q5. What is the coordination number of a central metal ion in an ideal octahedral complex?

• 4
• 6
• 8
• 12

Correct Answer: 6

Q6. Which geometry is most commonly adopted by d8 metal ions such as Pt(II) in many complexes?

• Tetrahedral
• Square planar
• Octahedral
• Trigonal bipyramidal

Correct Answer: Square planar

Q7. Bragg’s law relates X-ray wavelength, diffraction angle and which other quantity?

• Unit cell volume
• Miller index
• Interplanar spacing (d)
• Atomic number

Correct Answer: Interplanar spacing (d)

Q8. Which of the following is NOT a Miller index for a plane parallel to the c-axis in a cubic crystal?

• (1 0 0)
• (0 1 0)
• (0 0 1)
• (1 0 ∞)

Correct Answer: (1 0 ∞)

Q9. Which packing arrangement has the highest atomic packing factor (APF) among common cubic lattices?

• Body-centered cubic (BCC)
• Simple cubic (SC)
• Face-centered cubic (FCC)
• Hexagonal close-packed (HCP)

Correct Answer: Face-centered cubic (FCC)

Q10. The radius ratio rule helps predict which property of ionic crystals?

• Color
• Coordination number
• Magnetic moment
• Optical rotation

Correct Answer: Coordination number

Q11. In crystal field theory for octahedral complexes, which set of d orbitals is raised in energy?

• t2g
• eg
• p orbitals
• s orbital

Correct Answer: eg

Q12. Which ligand is higher in the spectrochemical series and causes larger splitting Δo: CN− or I−?

• CN−
• I−
• Both same
• Depends only on metal

Correct Answer: CN−

Q13. A complex with high crystal field splitting energy is more likely to be:

• High spin
• Low spin
• Paramagnetic with maximum unpaired electrons
• Always tetrahedral

Correct Answer: Low spin

Q14. Which type of isomerism involves different connectivity of ligands to a metal center?

• Geometrical isomerism
• Optical isomerism
• Linkage isomerism
• Conformational isomerism

Correct Answer: Linkage isomerism

Q15. Chelation generally increases complex stability due to which effect?

• Inductive effect
• Chelate effect (entropy gain)
• Steric hindrance only
• π-backbonding

Correct Answer: Chelate effect (entropy gain)

Q16. Polymorphism in pharmaceutical solids affects which key property most directly?

• Color only
• Solubility and dissolution rate
• Atomic number
• Magnetic susceptibility

Correct Answer: Solubility and dissolution rate

Q17. Which experimental technique provides direct atomic coordinates and 3D structure of a crystal?

• Powder X-ray diffraction (PXRD)
• Single crystal X-ray diffraction
• FTIR spectroscopy
• Ultraviolet spectroscopy

Correct Answer: Single crystal X-ray diffraction

Q18. In powder XRD patterns, peak positions primarily give information about:

• Molecular weight
• Interplanar spacings and unit cell dimensions
• Covalent bonding energies
• Absolute concentration

Correct Answer: Interplanar spacings and unit cell dimensions

Q19. Which defect type in crystals involves a missing ion or atom from its lattice site?

• Interstitial defect
• Vacancy defect
• Frenkel defect
• Substitutional impurity

Correct Answer: Vacancy defect

Q20. Frenkel defect is characterized by which combination?

• Vacancy and interstitial pair
• Two vacancies only
• Substitutional impurity and dislocation
• Grain boundary formation

Correct Answer: Vacancy and interstitial pair

Q21. Which of these is a common coordination geometry for coordination number 4?

• Octahedral only
• Tetrahedral and square planar
• Trigonal prismatic
• Cubic

Correct Answer: Tetrahedral and square planar

Q22. Miller indices (h k l) of the plane parallel to the x–y plane are:

• (0 0 1)
• (1 0 0)
• (0 1 0)
• (1 1 0)

Correct Answer: (0 0 1)

Q23. Which parameter directly determines the diffraction angle in Bragg’s law nλ = 2d sin θ?

• Electron configuration
• Interplanar spacing d
• Sample color
• Atomic mass

Correct Answer: Interplanar spacing d

Q24. A metal complex that shows optical activity (chirality) must lack which symmetry element?

• Rotation axis
• Mirror plane and inversion center
• Translation symmetry
• All proper axes

Correct Answer: Mirror plane and inversion center

Q25. Which crystalline hydrate contains coordinated water molecules directly bound to the metal center?

• Solvate with unbound solvent only
• Coordination hydrate
• Anhydrous salt
• Polymorph

Correct Answer: Coordination hydrate

Q26. In pharmaceutical crystallography, why is control of crystallization important?

• Only to change color
• To obtain the desired polymorph and particle properties affecting bioavailability
• To increase atomic number
• To change metal oxidation state

Correct Answer: To obtain the desired polymorph and particle properties affecting bioavailability

Q27. Which space group notation indicates the presence of a center of symmetry (inversion center)?

• P1
• P-1
• P2
• P4mm

Correct Answer: P-1

Q28. In ligand field splitting diagrams, which factor increases splitting Δo for an octahedral complex?

• Using weak field ligands like I−
• Using strong field ligands like CN−
• Decreasing metal oxidation state always
• Having all ligands monodentate only

Correct Answer: Using strong field ligands like CN−

Q29. Which technique is commonly used to detect polymorphs and identify crystalline phases in a drug sample?

• NMR spectroscopy
• Powder X-ray diffraction (PXRD)
• Liquid chromatography
• Mass spectrometry

Correct Answer: Powder X-ray diffraction (PXRD)

Q30. Which statement about coordination number and ligand size is generally true?

• Larger ligands favor higher coordination numbers
• Smaller ligands can allow higher coordination numbers
• Ligand size has no effect
• Only metal radius matters

Correct Answer: Smaller ligands can allow higher coordination numbers

Q31. Which of the following is a centrosymmetric point group often leading to achiral crystals?

• C1
• D2
• S4
• Ci

Correct Answer: Ci

Q32. What type of bonding predominates in ionic crystals like NaCl compared to coordination complexes?

• Covalent bonding only
• Ionic electrostatic interactions
• Metal–ligand dative bonding exclusively
• Hydrogen bonding only

Correct Answer: Ionic electrostatic interactions

Q33. Which defect increases ionic conductivity by providing mobile vacancies in ionic crystals?

• Dislocation
• Schottky defect
• Substitutional impurity that is neutral
• Grain boundary segregation only

Correct Answer: Schottky defect

Q34. Which of the following influences the stability of a crystalline drug complex in solid state?

• Environmental humidity and formation of hydrates
• Metal atomic number only
• Color of the packaging only
• Presence of noble gases

Correct Answer: Environmental humidity and formation of hydrates

Q35. In an octahedral d3 metal complex, how many unpaired electrons are expected in a strong-field case?

• 0
• 1
• 2
• 3

Correct Answer: 3

Q36. Which measurement can determine the thermal behavior and detect solvates or polymorphic transitions?

• Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)
• UV-visible spectroscopy
• NMR relaxation time
• Gel electrophoresis

Correct Answer: Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)

Q37. What does the term “unit cell parameters” refer to?

• Chemical name of the complex
• Cell edge lengths (a, b, c) and angles (α, β, γ)
• Number of electrons in metal
• Only the cell volume

Correct Answer: Cell edge lengths (a, b, c) and angles (α, β, γ)

Q38. Which metal–ligand interaction can give rise to π-backbonding affecting bond orders and wavelength of absorption?

• σ-donation only
• π-backbonding from metal d orbitals to ligand π* orbitals
• Hydrogen bonding to ligand
• Ionic electrostatic attraction only

Correct Answer: π-backbonding from metal d orbitals to ligand π* orbitals

Q39. Which ligand denticity term describes a ligand that can bind through two donor atoms?

• Monodentate
• Bidentate
• Polydentate
• Ambidentate only

Correct Answer: Bidentate

Q40. Which of the following is true about powder XRD peak broadening in small crystals or nanoparticles?

• Peak broadening decreases with smaller crystallite size
• Peak broadening increases with smaller crystallite size
• Peak position disappears entirely
• Peak intensity is independent of size

Correct Answer: Peak broadening increases with smaller crystallite size

Q41. The Wyckoff position in crystallography provides information about:

• Temperature of crystallization
• Symmetry-equivalent atomic positions within a space group
• Magnetic moment of ions
• Molar mass of the compound

Correct Answer: Symmetry-equivalent atomic positions within a space group

Q42. Which factor most directly affects whether a transition metal complex is labile or inert kinetically?

• Coordination number only
• Metal electronic configuration and ligand field strength
• Crystal system (cubic, tetragonal)
• Presence of Miller indices

Correct Answer: Metal electronic configuration and ligand field strength

Q43. Which of the following is an example of a linkage isomer in coordination chemistry?

• [Co(NH3)6]3+
• [SCN–] bound through S versus N giving thiocyanato and isothiocyanato isomers
• Tetrahedral vs square planar forms of the same complex
• Diastereomers from chiral ligands

Correct Answer: [SCN–] bound through S versus N giving thiocyanato and isothiocyanato isomers

Q44. Which property of a crystalline drug can be altered by forming a coordination complex with a metal ion?

• Only the elemental composition
• Solubility, stability and sometimes activity
• Only the crystalline color
• It cannot change any property

Correct Answer: Solubility, stability and sometimes activity

Q45. What is the primary reason single crystals are preferred for precise structure determination over powders?

• Cheaper to measure
• They allow measurement of individual reflections and full 3D intensity data
• Powder patterns contain no structural information
• Single crystals do not diffract X-rays

Correct Answer: They allow measurement of individual reflections and full 3D intensity data

Q46. In an FCC lattice, which plane family corresponds to the highest packing density commonly seen in close-packed structures?

• {100}
• {110}
• {111}
• {210}

Correct Answer: {111}

Q47. Which of the following describes isomorphous substitution in crystal chemistry?

• Replacement of one atom by another of similar size and charge without changing crystal structure
• Complete change of crystal system
• Substitution that always produces amorphous solids
• Only occurs for noble gases

Correct Answer: Replacement of one atom by another of similar size and charge without changing crystal structure

Q48. Which coordination geometry tends to be favored by 18-electron transition metal complexes for maximum stability?

• Square planar for all metals
• Octahedral for many d6 metals
• Tetrahedral for all d10 metals
• Linear for all d8 metals

Correct Answer: Octahedral for many d6 metals

Q49. Which analysis can distinguish between hydrate stoichiometries by measuring mass loss upon heating?

• Diffraction contrast tomography
• Thermogravimetric analysis (TGA)
• Circular dichroism
• Electrophoresis

Correct Answer: Thermogravimetric analysis (TGA)

Q50. Which concept explains why chelated metal complexes often have higher formation constants than monodentate analogs?

• Decrease in entropy upon chelation
• Entropy-driven chelate effect and multiple bond formation
• Only steric hindrance
• Because chelates are always smaller molecules

Correct Answer: Entropy-driven chelate effect and multiple bond formation

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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