Qualitative Chemistry Knowledge-based Questions and Answers
Welcome to qChem+, your trusted learning partner for NCTB HSC Chemistry! Chapter 2 of Chemistry 1st Paper — Qualitative Chemistry — is one of the most vital chapters for both HSC Board Exams and University Admission Tests (Engineering, Medical, and Public Universities).
In HSC Board examinations, Knowledge-based questions (1-mark questions) test your core fundamental definitions, formulas, laws, and symbols. Scoring full marks in these questions is the key to securing an A+ in Chemistry!
To help NCTB HSC English Version students excel, we have compiled and solved all the authentic knowledge questions from past Board Exams (2015–2026).
Check out the post below to get just these board exam questions in one place (without answers):
📌 1. Atomic Models & Fundamental Particles
1. What is an Isotone?
[SB 17]
Answer: Atoms that have the same number of neutrons but different atomic numbers (proton numbers) and mass numbers are called isotones of each other.
2. What is an Isotope?
[MB 25; RB 19; SB 17; RB 15]
Answer: Atoms that have the same atomic number (proton number) but different mass numbers are called isotopes of each other.
3. What is an α-particle (Alpha particle)?
[BB 25; CB 23; RB 22; CB 21; RB 19; CtgB, SB 17; RB 16; SB 16]
Answer: An alpha (α) particle is a doubly-charged positive helium nucleus (He²⁺).
📌 2. Quantum Numbers & Orbitals
4. What is a Quantum Number?
[MdB 26; Md(I)B 26; RB 25; DB 22; DinB, CtgB 21; JB, BB 16]
Answer: The set of four numbers used to specify the size, shape, 3D spatial orientation of an orbital, and the direction of spin of an electron on its own axis in an atom are called quantum numbers.
5. What is a Magnetic Quantum Number?
[CB 21]
Answer: The quantum number that indicates the three-dimensional spatial orientation of an orbital under the influence of an external magnetic field is called the magnetic quantum number (m).
6. What is a Sub-shell (Sub-energy level)?
[JB 17]
Answer: The specific energy levels within a principal energy level where electrons are distributed are called sub-shells or sub-energy levels (s, p, d, f).
7. What is an Orbit?
[MB 25; RB 22; DinB 21; CtgB 17; JB 15]
Answer: The fixed circular stationary paths around the atomic nucleus in which electrons revolve are called orbits.
8. What is a Node (Nodal Plane)?
[CtgB 26; SB 21; DinB 19]
Answer: The region or plane around the nucleus in an orbital where the probability of finding an electron is zero (0%) is called a node or nodal plane.
9. What is an Orbital?
[CtgB, BB 25; CtgB, MB, CB 23; MB, JB 22; DB, RB 21; BB 19; DB, RB, CB 17; SB 16]
Answer: The three-dimensional region around the nucleus where the probability of finding an electron is maximum (about 90%–95%) is called an orbital.
📌 3. Rules of Electronic Configuration
10. Write down the electronic configuration of Fe³⁺.
[SB 21]
Answer: Fe³⁺ (Atomic number 26, number of electrons 23): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵
11. What is the Aufbau Principle?
[MdB 26; CB 22; JB 21; RB 17]
Answer: In the ground state of an atom, electrons first enter the orbital of the lowest energy level and progressively fill orbitals of higher energy — this is the Aufbau principle.
12. What is Hund’s Rule?
[All.B 26; Md(I)B 26; DB, RB 25; DB, DinB, CtgB, BB 23; MB, JB, BB 22; SB 21; RB, JB 19; DinB 17]
Answer: Electron pairing in degenerate orbitals (orbitals of equal energy) will not occur until each orbital is singly occupied with electrons having parallel spins — this is Hund’s rule.
13. State Pauli’s Exclusion Principle.
[MB 23; SB 22; RB 21; CtgB 19; RB, JB, SB 17; RB, CB, CtgB 15]
Answer: No two electrons in the same atom can have the same set of all four quantum numbers (n, l, m, s).
📌 4. Electromagnetic Spectrum & Radiation
14. What is a Spectrum?
[CB, SB 25; CtgB, JB 22; RB, CB, CtgB, BB 18]
Answer: The pattern or array formed when light or electromagnetic radiation of various wavelengths passes through a prism or diffraction grating and separates according to wavelength is called a spectrum.
15. What is Electromagnetic Radiation?
[SB 22]
Answer: The propagation of energy through space in the form of waves generated by mutually perpendicular, oscillating electric and magnetic fields is called electromagnetic radiation.
16. What is an Electromagnetic Spectrum?
[JB 25]
Answer: The systematic arrangement of all types of electromagnetic radiation in increasing order of wavelength or frequency is called the electromagnetic spectrum.
17. What is a Line Spectrum (Atomic Emission Spectrum)?
[DB 25; RB 23]
Answer: The spectrum obtained by analyzing light emitted by excited atoms or ions, consisting of distinct, sharp isolated colored lines, is called a line spectrum or atomic spectrum.
18. What is the Stark Effect?
[JB 25]
Answer: The splitting of atomic spectral lines into finer components under the influence of an external electric field is called the Stark effect.
19. Write down the wavelength range of visible light.
[RB 17]
Answer: The wavelength range of visible light is 380 nm to 780 nm (or 3800 Å – 7800 Å).
20. What is the Zeeman Effect?
[DinB 25; DB, MB 21]
Answer: The splitting of atomic spectral lines into finer components under the influence of an external magnetic field is called the Zeeman effect.
21. What is Phosphorescence?
[DinB 25; JB 17]
Answer: The phenomenon where a substance absorbs radiation and continues to emit light for a prolonged duration even after the excitation source is removed is called phosphorescence.
📌 5. Solubility, Solubility Product & Ionic Product
22. What is a Saturated Solution?
[RB 23]
Answer: A solution that contains the maximum possible dissolved amount of solute at a given temperature in a specific quantity of solvent is called a saturated solution.
23. What is the Common Ion Effect?
[DB 16]
Answer: The suppression of the degree of ionization/dissociation of a weak electrolyte upon the addition of a strong electrolyte containing a common ion is called the common ion effect.
24. What is Ionic Product (Kᵢₚ)?
[DB, BB 25; DinB, BB 22; JB 17]
Answer: The product of the molar concentrations of constituent ions present in any solution (saturated, unsaturated, or supersaturated), raised to the power of their respective stoichiometric coefficients, is called the ionic product (Kᵢₚ).
25. What is Solubility Product (Kₛₚ)?
[RB 25; DinB 22; DB 21; DinB 17]
Answer: At a constant temperature, the product of the molar concentrations of constituent ions in a saturated solution of a sparingly soluble salt, raised to powers equal to their stoichiometric coefficients, is called the solubility product (Kₛₚ).
26. What is Solubility?
[Md(I)B 26; SB, BB 22; RB 21; DB, CB, SB 17; RB, BB 15]
Answer: The maximum mass of a solute in grams required to saturate 100 grams of a solvent at a specific temperature is called the solubility of that solute at that temperature.
📌 6. Qualitative Chemical Analysis & Separation Techniques
27. What is Nessler’s Reagent?
[RB 25; DinB, CtgB 22; JB 21; RB 17]
Answer: An alkaline solution of potassium tetraiodomercurate(II), K₂[HgI₄] dissolved in KOH or NaOH, is called Nessler’s reagent. (It is used for detecting ammonium ions, NH₄⁺).
28. What is Crystallization?
[MB, CtgB 21; DinB 19]
Answer: The process of isolating a solid solute from its hot saturated solution in the form of pure geometric crystals upon gradual cooling is called crystallization.
29. What is Fractional Distillation?
[JB 19; CB, CtgB, BB 18; SB 15; CB 17]
Answer: The process of separating two or more miscible liquids with close boiling points (difference less than 40°C) using a fractionating column based on their boiling point differences is called fractional distillation.
30. What is Steam Distillation?
[CtgB 26; DB 19]
Answer: The process of separating water-insoluble, steam-volatile organic compounds that decompose near their normal boiling point by passing steam through the mixture is called steam distillation.
31. What is Solvent Extraction?
[CB 19; SB 15]
Answer: The process of isolating a desired compound from an aqueous solution or mixture by shaking it with an immiscible organic solvent based on distribution coefficient differences is called solvent extraction.
32. What is Vacuum Distillation (Distillation under reduced pressure)?
[DinB 17]
Answer: The process of distilling high boiling point liquids that decompose at their normal boiling points by reducing the atmospheric pressure above the liquid is called vacuum distillation.
33. What is Chromatography?
[CtgB 19; CB, CtgB, BB 18; CtgB 16; RB, BB 15]
Answer: A physical method of separation in which components of a mixture are separated based on their relative distribution between two immiscible phases — a stationary phase and a mobile phase — is called chromatography.
34. What is Retention Factor (R𝒇)?
[All. B 26; SB 19; SB 17; DinB 15]
Answer: In chromatography, the ratio of the distance travelled by the sample component to the distance travelled by the solvent front is called the Retention Factor (R𝒇).
Abbreviations used: All.B = All Board, DB = Dhaka, RB = Rajshahi, CB = Comilla, JB = Jessore, CtgB = Chittagong, BB = Barisal, SB = Sylhet, DinB = Dinajpur, MB = Mymensingh, MdB = Madrasah, Md(I)B = Madrasah (Irregular).
💡 Top Exam Preparation Tips from qChem+:
- Practice Board Tagged Questions: Revise these 34 core questions repeatedly — they represent over 90% of the recurring knowledge-based questions in HSC Board Exams.
- Pay Attention to Symbols & Charges: Ensure accurate representation of chemical formulas, charges (e.g., Fe³⁺, He²⁺, NH₄⁺), quantum numbers, and mathematical expressions.
- Bookmark & Share: Keep qChem+ bookmarked for more English Version HSC Chemistry study notes, board solutions, and admission prep resources!
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