BPSC CCE Prelims
Chemistry Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Chemistry
Topic Breakdown: Scroll →
Which of the following are the constituents of a soda acid fire extinguisher?
Detailed Explanation:
Soda acid fire extinguisher contains dilute sulphuric acid (H₂SO₄) and sodium bicarbonate (NaHCO₃) solution in separate compartments.
When activated, the acid reacts with sodium bicarbonate: 2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂, producing carbon dioxide gas that smothers the fire by cutting off oxygen supply.
Option 3 is correct.
Which one of the following is an example of melamine used for making floor tiles?
Detailed Explanation:
Melamine is a thermo-setting plastic that undergoes irreversible hardening when heated, forming a rigid three-dimensional network.
Used in floor tiles, kitchenware, and laminates, melamine-formaldehyde resin is heat-resistant, scratch-proof, and does not soften upon reheating. Polyethene, thermoplastics, and PVC are thermoplastics that soften when heated and can be remolded.
Which of the following is the first artificially prepared element?
Detailed Explanation:
Technetium (Tc) is the first artificially prepared element, synthesized in 1937 by Carlo Perrier and Emilio Segrè by bombarding molybdenum with deuterons in a cyclotron.
Tellurium (Te), Thorium (Th), and Thallium (Tl) are all naturally occurring elements found in Earth's crust.
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Which among the following is a positively charged particle emitted by a radioactive element?
Detailed Explanation:
Alpha particles (α) are positively charged particles emitted during radioactive decay, consisting of 2 protons + 2 neutrons (essentially a helium nucleus).
Beta rays (β) are negatively charged electrons, while cathode rays are also streams of electrons, both carrying negative charge.
Therefore, Option 3 (Alpha ray) is the correct answer.
A form of matter has no fixed shape but it has a fixed volume. An example of this form of matter is
Detailed Explanation:
Matter with no fixed shape but fixed volume is a liquid.
✅ Kerosene is a liquid – has fixed volume but takes the shape of its container.
❌ Carbon steel is a solid – has both fixed shape and fixed volume.
❌ Krypton is a noble gas – has neither fixed shape nor fixed volume.
Some metal oxides react with acid as well as a base to produce salt and water. They are known as amphoteric oxides. Examples of amphoteric oxides are
Detailed Explanation:
Amphoteric oxides react with both acids and bases to form salt and water.
✅ Al₂O₃ (Aluminium oxide) reacts with HCl to give AlCl₃ + H₂O and with NaOH to give NaAlO₂ + H₂O.
✅ ZnO (Zinc oxide) reacts with H₂SO₄ to give ZnSO₄ + H₂O and with NaOH to give Na₂ZnO₂ + H₂O.
❌ CuO (Copper oxide) is a basic oxide that reacts only with acids, not with bases.
Therefore, Option 2 (Al₂O₃ and ZnO) is the correct answer.
Acids react with metal carbonates to liberate ______ gas.
Detailed Explanation:
When acids react with metal carbonates, the general reaction is: Acid + Metal Carbonate → Salt + Water + CO₂.
For example, HCl + CaCO₃ → CaCl₂ + H₂O + CO₂, producing carbon dioxide gas (CO₂) which is observed as effervescence (bubbles).
Which acid is described as HOOCCOOH?
Detailed Explanation:
HOOCCOOH is the chemical formula for Oxalic acid, a dicarboxylic acid with two carboxyl groups (-COOH).
Carbonic acid is H₂CO₃, Acetic acid is CH₃COOH, making Option 2 the only correct answer.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. Which of them will turn red litmus to blue?
Detailed Explanation:
Red litmus paper turns blue only in the presence of a basic (alkaline) solution.
Distilled water is neutral (pH 7) and does not change litmus colour; acidic solutions turn blue litmus red, not the reverse; only bases have the chemical property to convert red litmus to blue.
The odour of acetic acid resembles that of
Detailed Explanation:
Acetic acid is the main component of vinegar, giving it its characteristic pungent, sour smell.
Vinegar typically contains 4-8% acetic acid by volume, which is why the odour of pure acetic acid closely resembles that of vinegar.
Why does dry HCI gas not change the colour of dry litmus paper?
Detailed Explanation:
Dry HCl gas does not ionize to produce H₃O⁺ (hydronium) ions because ionization requires the presence of water molecules.
Litmus paper changes colour only when H₃O⁺ ions are present in solution; dry HCl remains molecular (HCl) and cannot act as an acid without water to donate protons to.
Detect the odd one.
Detailed Explanation:
✅ Option 1 – Ripening of fruit: This is an irreversible change (fruit cannot be un-ripened).
✅ Option 2 – Setting of cement: This is an irreversible change (cement cannot return to powder form once set).
✅ Option 3 – Burning of coal: This is an irreversible change (coal once burned cannot be recovered).
All three options represent irreversible changes, so none of them is the odd one out. Hence, Option 5 (None of the above) is correct.
Which of the following statements about diamond and graphite is true?
Detailed Explanation:
❌ Statement 1 – Incorrect: Diamond is an electrical insulator (no free electrons), while graphite is a good electrical conductor (has delocalized electrons in layers).
❌ Statement 2 – Incorrect: Diamond has a tetrahedral crystal structure (each carbon bonded to 4 others in 3D), while graphite has a hexagonal layered structure (each carbon bonded to 3 others in 2D layers).
❌ Statement 3 – Incorrect: Diamond is the hardest natural substance (Mohs scale 10), while graphite is soft and slippery (Mohs scale 1-2) due to weak van der Waals forces between layers.
Both are allotropes of carbon with vastly different physical properties due to different atomic arrangements.
The nucleus of an atom consists of
Detailed Explanation:
The nucleus of an atom contains protons (positively charged) and neutrons (neutral), forming the dense central core discovered by Rutherford in 1911.
Electrons orbit outside the nucleus in electron clouds—they are not part of the nuclear structure.
Therefore, only protons and neutrons constitute the nucleus, making Option 2 the correct answer.
The metallurgical process in which a metal is obtained in a fused state is called
Detailed Explanation:
Smelting is the metallurgical process where ore is heated with a reducing agent (like coke) to extract the metal in a fused (molten) state, separated from slag.
Roasting converts sulfides to oxides in excess air, calcination removes volatile impurities in limited air, and froth flotation is a physical concentration method—none produce molten metal directly.
Therefore, only smelting yields metal in a fused state, making Option 4 the correct answer.