BPSC CCE Prelims
Chemistry Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Chemistry
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Standard electrode potential of three metals A, B and C are respectively 0.5 V, -3 V and -1.2 V. Reducing power of these metals would be
Detailed Explanation:
Reducing power is inversely related to standard electrode potential (E°) — the more negative the E°, the stronger the reducing agent.
Metal B (−3.0 V) has the most negative potential → highest reducing power. Metal C (−1.2 V) is moderately negative → intermediate reducing power. Metal A (+0.5 V) is positive → lowest reducing power. Order: B > C > A.
Sour taste of vinegar is due to
Detailed Explanation:
The sour taste of vinegar is due to acetic acid (CH₃COOH), which is produced by fermentation of ethanol.
Tartaric acid is found in tamarind and grapes, lactic acid in sour milk and curd, and citric acid in citrus fruits — none of these is the acid in vinegar.
pH value of 0.1N HCl solution is approximately:
Detailed Explanation:
HCl is a strong acid that dissociates completely: HCl → H⁺ + Cl⁻. For a monoprotic acid, 0.1N = 0.1M, so [H⁺] = 0.1 M.
pH = -log[H⁺] = -log(0.1) = -(-1) = 1.0. Options with pH 10 or 11 indicate basic solutions, not acids. pH 2.0 would require [H⁺] = 0.01 M, which is ten times more dilute.
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Which Compound is known as night glowing pigment from below?
Detailed Explanation:
Europium-doped strontium aluminate (SrAl₂O₄:Eu²⁺,Dy³⁺) is the most efficient modern phosphorescent material used in night glowing pigments.
It absorbs light energy and slowly releases it in darkness, providing a bright afterglow lasting up to 12 hours. Other compounds listed (copper sulphide-doped zinc oxide, barium sulphate-doped copper carbonate, boron oxide-doped copper sulphate) do not exhibit significant or efficient phosphorescence for glow-in-the-dark applications.
Why oil is not stored in galvanized iron pot?
Detailed Explanation:
Galvanized iron is coated with zinc, which reacts with oil components to form toxic zinc compounds that make the oil unsafe for consumption.
The chemical reaction also causes rancidity, degrading the oil's taste, smell, and nutritional quality.
Moisture and acidic impurities in oil corrode the zinc coating, exposing the underlying iron to rust formation.
Since all three effects—toxicity, quality degradation, and corrosion—occur simultaneously, the correct answer is All of above.
Which compound is used for increase of octane rating?
Detailed Explanation:
Tetraethyllead (TEL) was historically the most widely used anti-knock agent added to gasoline to increase octane rating and prevent engine knocking.
Though highly effective, TEL is toxic and has been phased out globally; modern fuels use unleaded alternatives like ethanol and aromatic hydrocarbons.
Catalyst used in hydrogenation of vegetable oil into vanaspati ghee is
Detailed Explanation:
Nickel (Ni) is the industrial catalyst used in the hydrogenation of vegetable oils to produce vanaspati ghee.
The process converts unsaturated fats (liquid oils) into saturated fats (solid ghee) by adding hydrogen in the presence of finely divided nickel at 140–225°C.
Which of the following is not an electrophile?
Detailed Explanation:
Electrophiles are electron-deficient species that accept electron pairs, typically carrying a positive charge or having an incomplete octet.
Na⁺ (sodium ion) has a stable noble-gas configuration (1s²2s²2p⁶) with no empty orbitals available to accept electrons, making it a spectator ion rather than an electrophile.
BF₃ (boron trifluoride) has an incomplete octet on boron (only 6 electrons), allowing it to act as a Lewis acid and electrophile.
H⁺ (proton) has no electrons and readily accepts electron pairs, making it a strong electrophile.
The conductivity of a strong electrolyte
Detailed Explanation:
Conductivity (specific conductivity) measures the ability of a unit volume of solution to conduct electricity, depending on number of ions per unit volume.
On dilution, total ions remain constant but volume increases, so ion concentration per unit volume decreases, causing conductivity to decrease. (Note: Molar conductivity increases with dilution, but the question asks about conductivity.)
For two liquids A and B to form an ideal solution
Detailed Explanation:
An ideal solution follows Raoult's law where intermolecular forces between A–A, B–B, and A–B molecules are approximately equal.
Enthalpy of mixing (ΔHmix) = 0 because no heat is absorbed or released during mixing.
Entropy of mixing (ΔSmix) > 0 (positive) due to increased randomness, and Free energy of mixing (ΔGmix) < 0 (negative), making the process spontaneous.
Which of the following are exothermic processes?
i. Evaporation of water.
ii. Dilution of an acid (H2SO4).
iii. Reaction of water with quick lime.
iv. Sublimation of camphor (crystals).
Detailed Explanation:
Exothermic processes release heat to surroundings; endothermic processes absorb heat.
i. Evaporation of water – absorbs heat from surroundings (endothermic).
ii. Dilution of H₂SO₄ – releases large amount of heat when water is added (exothermic).
iii. Reaction of water with quick lime (CaO) – forms slaked lime with vigorous heat release (exothermic).
iv. Sublimation of camphor – solid to gas transition requires heat absorption (endothermic).
Only ii and iii are exothermic.
Which of the following pairs will give displacement reactions?
Detailed Explanation:
Displacement reactions occur when a more reactive metal displaces a less reactive metal from its salt solution.
Copper (Cu) is more reactive than silver (Ag) but less reactive than sodium (Na), iron (Fe), and magnesium (Mg). Therefore, Cu can displace Ag from AgNO₃ solution, forming Cu(NO₃)₂ and depositing metallic Ag.
In other options: Cu cannot displace Na (option 2), Ag cannot displace Fe (option 3), and Al cannot displace Mg (option 4) due to reactivity series order.
Who was the first one to propose a model for the structure of an atom?
Detailed Explanation:
J.J. Thomson proposed the first atomic model in 1897, known as the plum pudding model, with electrons embedded in a positively charged sphere.
E. Goldstein discovered canal rays, Rutherford proposed the nuclear model in 1911, and Niels Bohr introduced the planetary model with fixed orbits in 1913.
Dalton's atomic theory successfully explained:
i. Law of conservation of mass
ii. Law of constant composition
iii. Law of radioactivity
iv. Law of multiple proportion
Detailed Explanation:
Dalton's atomic theory (1808) explained three fundamental laws of chemical combination:
✅ Law of conservation of mass: Atoms are neither created nor destroyed in reactions, so total mass remains constant.
✅ Law of constant composition: A compound always contains the same elements in fixed proportions by mass.
✅ Law of multiple proportions: When two elements form multiple compounds, mass ratios are simple whole numbers.
❌ Law of radioactivity: Radioactivity (discovered by Becquerel, 1896) involves nuclear changes, not explained by Dalton's indivisible atom concept.
Which of the following represents the suitable condition for the liquefaction of gases?
Detailed Explanation:
Low temperature reduces the kinetic energy of gas molecules, allowing intermolecular attractive forces to dominate.
High pressure brings molecules closer together, decreasing intermolecular distance and facilitating condensation into liquid phase. Each gas has a critical temperature above which liquefaction is impossible regardless of pressure.