Structure and uses of formaldehyde MCQs With Answer

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Structure and uses of formaldehyde MCQs With Answer

Formaldehyde (methanal, CH2O) is a simple aldehyde with wide pharmaceutical relevance. This introduction covers its molecular structure, reactivity (carbonyl group, sp2 hybridized carbon), polymerization to paraformaldehyde and trioxane, common formulations like formalin, and major uses as a fixative, disinfectant, and precursor to resins (urea‑formaldehyde, phenol‑formaldehyde). For B. Pharm students, understanding mechanisms of protein cross‑linking, common reactions (Cannizzaro, nucleophilic addition), safety, and regulatory concerns (toxicity, carcinogenicity) is essential. The following MCQs focus on structural features, reactions, applications, handling, and clinical/laboratory relevance. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which is the correct molecular formula of formaldehyde?

  • CH4O
  • CH2O
  • CH3O
  • C2H4O

Correct Answer: CH2O

Q2. What is the IUPAC name of formaldehyde?

  • Methanol
  • Formic aldehyde
  • Methanal
  • Formaldehyde (IUPAC not assigned)

Correct Answer: Methanal

Q3. What is the hybridization of the carbonyl carbon in formaldehyde?

  • sp
  • sp2
  • sp3
  • sp3d

Correct Answer: sp2

Q4. Which of the following describes the geometry around the carbonyl carbon of formaldehyde?

  • Tetrahedral
  • Linear
  • Trigonal planar
  • Octahedral

Correct Answer: Trigonal planar

Q5. At room temperature, pure formaldehyde is primarily found as:

  • Aqueous solution only
  • Colorless gas
  • White crystalline solid
  • Thick syrup

Correct Answer: Colorless gas

Q6. Formalin typically refers to which concentration of aqueous formaldehyde?

  • 5% w/v
  • 10% w/v
  • 37% w/v
  • 50% w/v

Correct Answer: 37% w/v

Q7. Neutral buffered formalin (10% NBF) contains approximately what percentage of formaldehyde?

  • 1% formaldehyde
  • 4% formaldehyde
  • 10% formaldehyde
  • 37% formaldehyde

Correct Answer: 4% formaldehyde

Q8. Which functional group is present in formaldehyde?

  • Carboxyl
  • Aldehyde
  • Ketone
  • Alcohol

Correct Answer: Aldehyde

Q9. Formaldehyde reacts with primary amines to form which intermediate class of compounds?

  • Hydrazones
  • Imine (Schiff base)
  • Alcohols
  • Ketals

Correct Answer: Imine (Schiff base)

Q10. Which reaction is characteristic of formaldehyde due to absence of alpha hydrogens?

  • Aldol condensation
  • Cannizzaro reaction
  • Claisen rearrangement
  • Perkin reaction

Correct Answer: Cannizzaro reaction

Q11. Formaldehyde polymerizes to form which linear polymer used as a preservative?

  • Polyethylene
  • Paraformaldehyde
  • Polyacrylamide
  • Polystyrene

Correct Answer: Paraformaldehyde

Q12. The cyclic trimer of formaldehyde with commercial importance is called:

  • Trioxane
  • Acetaldehyde
  • Formic anhydride
  • Ethylene oxide

Correct Answer: Trioxane

Q13. Which of the following is a major industrial use of formaldehyde?

  • Fuel additive
  • Production of resins and adhesives
  • Primary solvent for chromatography
  • Replacement for ethanol in sanitizers

Correct Answer: Production of resins and adhesives

Q14. Formaldehyde is widely used in histology primarily as a:

  • Stain
  • Fixative
  • Embedding medium
  • Sectioning aid

Correct Answer: Fixative

Q15. The primary mechanism by which formaldehyde fixes tissues is:

  • Denaturation by dehydration only
  • Covalent cross‑linking of proteins (methylene bridges)
  • Oxidative cleavage of lipids
  • Formation of ionic bonds with nucleic acids

Correct Answer: Covalent cross‑linking of proteins (methylene bridges)

Q16. Which safety classification applies to formaldehyde regarding carcinogenicity?

  • Not classifiable
  • Probably not carcinogenic
  • Possibly carcinogenic to humans
  • Carcinogenic to humans (IARC Group 1)

Correct Answer: Carcinogenic to humans (IARC Group 1)

Q17. A positive Tollens’ test indicates presence of which functional group that formaldehyde possesses?

  • Carboxylic acid
  • Alcohol
  • Aldehyde
  • Ketone

Correct Answer: Aldehyde

Q18. Which compound is formed when formaldehyde is oxidized in air or chemically?

  • Formic acid
  • Methanol
  • Acetic acid
  • Formamide

Correct Answer: Formic acid

Q19. Reduction of formaldehyde yields which product?

  • Methane
  • Formic acid
  • Methanol
  • Ethanol

Correct Answer: Methanol

Q20. Which of the following tests is commonly used to detect formaldehyde in the laboratory?

  • Ninhydrin test
  • Schiff’s reagent
  • Biuret test
  • Coomassie blue

Correct Answer: Schiff’s reagent

Q21. Formaldehyde’s odor threshold and irritant effects are important for safety. It mainly irritates which of the following?

  • Dermis only
  • Eyes, nose and respiratory tract
  • Inner ear
  • Gastrointestinal tract exclusively

Correct Answer: Eyes, nose and respiratory tract

Q22. Urea‑formaldehyde resins are commonly used in:

  • Pharmaceutical tablet coating
  • Plywood and particleboard adhesives
  • Intravenous fluids
  • Oral syrups

Correct Answer: Plywood and particleboard adhesives

Q23. Which of the following statements about paraformaldehyde is true?

  • It is an oligomer of methanol
  • It is the polymeric form of formaldehyde used as a solid preservative
  • It is a trimeric cyclic ether
  • It is a reducing sugar

Correct Answer: It is the polymeric form of formaldehyde used as a solid preservative

Q24. In aqueous solution, formaldehyde exists predominantly as:

  • Methanol
  • Hydrated gem‑diol (methylene glycol)
  • Acetal form
  • Free radical

Correct Answer: Hydrated gem‑diol (methylene glycol)

Q25. Which regulatory precaution is essential when handling concentrated formaldehyde?

  • No special precautions required
  • Use of fume hood and PPE (gloves, goggles, respirator)
  • Store at high temperature
  • Mix with strong acids before use

Correct Answer: Use of fume hood and PPE (gloves, goggles, respirator)

Q26. Formaldehyde cross‑linking is useful in vaccine production because it:

  • Enhances microbial growth
  • Inactivates pathogens while preserving antigenic structure
  • Acts as an adjuvant to boost immunity
  • Serves as a nutrient source

Correct Answer: Inactivates pathogens while preserving antigenic structure

Q27. Which derivative is formed by reacting formaldehyde with phenol under acid catalysis?

  • Urea‑formaldehyde resin
  • Phenol‑formaldehyde resin (Bakelite type)
  • Polyethylene
  • Polylactic acid

Correct Answer: Phenol‑formaldehyde resin (Bakelite type)

Q28. Which of the following is NOT a common use of formaldehyde in pharmacy and laboratories?

  • Tissue fixation
  • Disinfection of equipment
  • Tablet filler component
  • Preservation of biological specimens

Correct Answer: Tablet filler component

Q29. Formaldehyde reacts readily with thiol groups (-SH) in proteins to form:

  • Disulfide bonds
  • Thioethers or cross‑links via methylene bridges
  • Carboxylic acids
  • Phosphates

Correct Answer: Thioethers or cross‑links via methylene bridges

Q30. The pungent odor of formaldehyde is primarily due to which small molecule?

  • Hydrogen sulfide
  • Formaldehyde itself
  • Methane
  • Ammonia

Correct Answer: Formaldehyde itself

Q31. Which laboratory practice reduces exposure to airborne formaldehyde?

  • Working in a closed cupboard without ventilation
  • Performing procedures in a certified chemical fume hood
  • Heating formaldehyde to increase evaporation
  • Using higher concentrated solutions in open air

Correct Answer: Performing procedures in a certified chemical fume hood

Q32. Formaldehyde is classified as which type of electrophile due to its carbonyl carbon?

  • Soft electrophile
  • Hard electrophile
  • Radical electrophile
  • Non‑electrophilic

Correct Answer: Hard electrophile

Q33. In the synthesis of drugs, formaldehyde is commonly used to introduce which group or linkage?

  • Alkyl chloride
  • Methylene (-CH2-) bridge or methylol group
  • Carboxylate ester
  • Aromatic halide

Correct Answer: Methylene (-CH2-) bridge or methylol group

Q34. Which symptom is an acute sign of formaldehyde inhalation?

  • Hypertension without respiratory symptoms
  • Coughing and eye irritation
  • Immediate loss of balance only
  • Skin tanning

Correct Answer: Coughing and eye irritation

Q35. Which analytical method can quantify formaldehyde in environmental samples?

  • Gas chromatography with derivatization
  • Simple pH paper
  • Oscillating balance
  • Mass balance of solids only

Correct Answer: Gas chromatography with derivatization

Q36. Which of the following best explains why formaldehyde is effective as a preservative?

  • It feeds microbial growth stabilizing specimens
  • It cross‑links and denatures microbial proteins and enzymes, inhibiting decomposition
  • It acts as a weak acid to lower pH only
  • It dissolves biological tissues instantly

Correct Answer: It cross‑links and denatures microbial proteins and enzymes, inhibiting decomposition

Q37. Which product is formed when formaldehyde reacts with ethanol under acidic conditions?

  • Hemiformal/acetal (1,1‑diethoxy methane derivative)
  • Ethylene glycol
  • Acetone
  • Acetic acid

Correct Answer: Hemiformal/acetal (1,1‑diethoxy methane derivative)

Q38. Which occupational exposure limit is most relevant to formaldehyde safety (general concept)?

  • Time‑weighted average (TWA) and short‑term exposure limit (STEL)
  • Only an annual exposure limit
  • No limits exist for formaldehyde
  • Only a chronic exposure index with no short‑term values

Correct Answer: Time‑weighted average (TWA) and short‑term exposure limit (STEL)

Q39. Which common pharmaceutical material can release formaldehyde slowly and is used as a preservative?

  • Parabens
  • Formaldehyde‑releasing agents (e.g., DMDM hydantoin)
  • Sucrose
  • Glycerin

Correct Answer: Formaldehyde‑releasing agents (e.g., DMDM hydantoin)

Q40. In histopathology, why is buffered formalin preferred over unbuffered formalin?

  • Buffered formalin is more acidic to speed fixation
  • Buffering prevents formalin from converting to formic acid and causing tissue artefacts
  • Unbuffered formalin is nonreactive
  • Buffered formalin dissolves tissues faster

Correct Answer: Buffering prevents formalin from converting to formic acid and causing tissue artefacts

Q41. Which type of chemical bond is mainly formed between formaldehyde and lysine residues in proteins?

  • Disulfide bond
  • Methylene bridge (‑CH2‑) crosslink between amino groups
  • Phosphodiester bond
  • Glycosidic bond

Correct Answer: Methylene bridge (‑CH2‑) crosslink between amino groups

Q42. The characteristic carbonyl stretching frequency of aldehydes in IR spectroscopy appears approximately at:

  • 1700 cm‑1 (typical carbonyl region)
  • 3200 cm‑1
  • 1500 cm‑1
  • 6000 cm‑1

Correct Answer: 1700 cm‑1 (typical carbonyl region)

Q43. Which solvent is commonly used to store paraformaldehyde before depolymerization to obtain formaldehyde solution?

  • Acetone
  • Hot water (aqueous solution)
  • Hexane
  • Ether

Correct Answer: Hot water (aqueous solution)

Q44. Formaldehyde-based fumigants like trioxane are used for:

  • Surface cleaning of metallic implants only
  • Disinfection and fumigation of enclosed spaces
  • Direct intravenous sterilization
  • Oral antiseptics

Correct Answer: Disinfection and fumigation of enclosed spaces

Q45. Which metabolic fate of inhaled formaldehyde is most relevant in humans?

  • It is largely metabolized at the site of entry and does not reach systemic circulation in high amounts
  • It circulates unchanged to all tissues
  • It is converted to benzene in vivo
  • It accumulates in adipose tissue

Correct Answer: It is largely metabolized at the site of entry and does not reach systemic circulation in high amounts

Q46. Which reagent is commonly used to derivatize formaldehyde for chromatographic analysis?

  • 2,4‑Dinitrophenylhydrazine (DNPH)
  • Bromothymol blue
  • Nitroprusside
  • Biuret reagent

Correct Answer: 2,4‑Dinitrophenylhydrazine (DNPH)

Q47. Which statement is true regarding formaldehyde and microbial sterilization?

  • Formaldehyde is ineffective against spores
  • Formaldehyde gas is a potent sporicide under controlled conditions
  • Formaldehyde is only a fungicide
  • Formaldehyde cannot inactivate viruses

Correct Answer: Formaldehyde gas is a potent sporicide under controlled conditions

Q48. In synthesis, formaldehyde can act as a one‑carbon (C1) building block to introduce what functional unit?

  • Methylene or hydroxymethyl group (-CH2- or -CH2OH)
  • Ethyl group (-C2H5)
  • Nitro group (-NO2)
  • Phenyl ring

Correct Answer: Methylene or hydroxymethyl group (-CH2- or -CH2OH)

Q49. Which precaution is recommended for long‑term storage of formalin solutions?

  • Store at elevated temperature to prevent polymerization
  • Keep tightly sealed, cool and away from light to reduce oxidation and polymer formation
  • Mix with strong acids before storage
  • Store in open containers to allow volatilization

Correct Answer: Keep tightly sealed, cool and away from light to reduce oxidation and polymer formation

Q50. Which of the following best summarizes the importance of understanding formaldehyde for B. Pharm students?

  • It is rarely used and of little pharmaceutical relevance
  • Knowledge is essential because formaldehyde is widely used as a fixative, preservative, resin precursor, and poses important safety and regulatory concerns
  • It is only relevant for food chemistry
  • It is only a cosmetic ingredient without hazards

Correct Answer: Knowledge is essential because formaldehyde is widely used as a fixative, preservative, resin precursor, and poses important safety and regulatory concerns

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