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Q1. A solution turning red litmus blue has pH close to:
Red litmus turns blue in basic solutions. Basic solutions have pH greater than 7. Among the options, pH 10 is basic (alkaline). pH 5, 4, and 1 are all acidic (pH < 7). So pH 10 is correct.
Q2. Washing soda is used to remove:
Washing soda (Na₂CO₃·10H₂O) is used to remove permanent hardness of water. It reacts with soluble calcium and magnesium salts (which cause permanent hardness) to form insoluble carbonates that precipitate out. Temporary hardness is removed by boiling. So permanent hardness is correct.
Q3. Plaster of Paris is chemically:
Plaster of Paris is chemically calcium sulphate hemihydrate, with the formula CaSO₄·½H₂O. It is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K. Calcium oxide is quick lime, calcium sulphate is anhydrous, calcium carbonate is limestone. So calcium sulphate hemihydrate is correct.
Q4. Distilled water does not conduct electricity because it:
Distilled water does not conduct electricity because it contains no ions (or very few due to self-ionisation). Electrical conductivity requires charged particles (ions) to carry current. Being neutral, pure, or colourless are not the reasons. So has no ions is correct.
Q5. Plaster of Paris is named so because:
Plaster of Paris is named because gypsum (from which it is made) was found in large deposits near Paris, France. It was not invented by doctors, discovered in Paris as a city, or first used in Paris as a location. So gypsum deposits near Paris were used is correct.
Q6. Washing soda has the chemical formula:
Washing soda is sodium carbonate decahydrate with the formula Na₂CO₃·10H₂O. NaHCO₃ is baking soda, Na₂CO₃ is anhydrous sodium carbonate, NaOH is sodium hydroxide. So Na₂CO₃·10H₂O is correct.
Q7. Plaster of Paris reacts with water to form:
Plaster of Paris (CaSO₄·½H₂O) reacts with water to form gypsum (CaSO₄·2H₂O). The reaction is: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. This is an exothermic reaction and causes the plaster to set hard. Calcium oxide is quick lime, calcium carbonate is limestone. So gypsum is correct.
Q8. Washing soda is used in:
Washing soda (Na₂CO₃·10H₂O) has many industrial uses. It is used in the glass industry (as a flux), soap industry (as a cleansing agent), and paper industry (in pulping and bleaching). So all of these is correct.
Q9. On heating copper sulphate crystals, their colour becomes:
Copper sulphate crystals (CuSO₄·5H₂O) are blue due to water of crystallisation. On heating, they lose water and become white anhydrous copper sulphate (CuSO₄). The reaction is: CuSO₄·5H₂O → CuSO₄ + 5H₂O. So white is correct.
Q10. Heating NaHCO₃ produces carbon dioxide, water and:
On heating sodium hydrogen carbonate (NaHCO₃), it decomposes to give sodium carbonate (Na₂CO₃), carbon dioxide (CO₂), and water (H₂O). The reaction is: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O. Sodium oxide, sodium hydroxide, and sodium chloride are not formed. So sodium carbonate is correct.
Q11. Baking soda added to milk delays curd formation because:
Curd formation occurs when bacteria produce lactic acid, which makes milk acidic. Adding baking soda (a base) neutralises the acid and makes the milk slightly basic. This delays the curd formation because bacteria need acidic conditions to grow. It does not increase acidity, kill bacteria, or remove lactose. So it makes milk basic is correct.
Q12. Acid reacting with metal carbonate produces:
When an acid reacts with a metal carbonate, it produces a salt, water, and carbon dioxide gas. For example: Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O. Salt and hydrogen is from acid + metal, salt and water is from acid + base. So salt, water and CO₂ is correct.
Q13. Sodium hydrogen carbonate is used in:
Sodium hydrogen carbonate (NaHCO₃, baking soda) has multiple uses: in fire extinguishers (releases CO₂ to smother fire), in baking powder (leavening agent), and as an antacid (neutralises stomach acid). So all of these is correct.
Q14. Plaster of Paris is obtained by heating gypsum at:
Plaster of Paris is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K (100°C). At this temperature, gypsum loses water to form calcium sulphate hemihydrate: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. 473 K is too high (would form anhydrous calcium sulphate), 273 K is freezing point, 300 K is room temperature. So 373 K is correct.
Q15. Water of crystallisation is:
Water of crystallisation is the fixed number of water molecules that are chemically bonded to the salt in its crystalline structure. For example, CuSO₄·5H₂O has 5 water molecules per formula unit. It is not dissolved water, surface moisture, or free water. So fixed number of water molecules in salt is correct.
Q16. Washing soda is obtained by recrystallisation of:
Washing soda (Na₂CO₃·10H₂O) is obtained by the recrystallisation of sodium carbonate (Na₂CO₃). Sodium carbonate is dissolved in water and allowed to crystallise, forming washing soda. Sodium hydroxide, sodium chloride, and baking powder are not used for this purpose. So sodium carbonate is correct.
Q17. Chemical formula of Plaster of Paris is:
Plaster of Paris is calcium sulphate hemihydrate with the formula CaSO₄·½H₂O. CaSO₄·2H₂O is gypsum, CaSO₄ is anhydrous calcium sulphate, CaCO₃ is calcium carbonate. So CaSO₄·½H₂O is correct.
Q18. Washing soda is a:
Washing soda (Na₂CO₃) is a salt formed from a strong base (NaOH) and a weak acid (H₂CO₃). Such salts are basic in nature with pH > 7. It is not acidic, neutral, or amphoteric. So basic salt is correct.
Q19. Acidic and basic solutions conduct electricity because they produce:
Acidic and basic solutions conduct electricity because they dissociate into ions (charged particles) in water. These ions carry electric current. Molecules and atoms are neutral and do not conduct. Electrons are not free in solution like in metals. So ions is correct.
Q20. The gas responsible for making cakes and bread fluffy is:
Baking powder or baking soda releases carbon dioxide (CO₂) gas when heated or mixed with acidic ingredients. The CO₂ bubbles get trapped in the dough, making cakes and bread fluffy and soft. Nitrogen, hydrogen, and oxygen do not do this. So carbon dioxide is correct.
Q21. Sodium hydrogen carbonate neutralises stomach acid because it is:
Sodium hydrogen carbonate (NaHCO₃) is a mild base. It neutralises excess stomach acid (HCl) by reacting with it: NaHCO₃ + HCl → NaCl + CO₂ + H₂O. It is not neutral, corrosive, or acidic. So basic is correct.
Q22. Baking powder contains baking soda and:
Baking powder contains baking soda (NaHCO₃) and a mild edible acid like tartaric acid. When water is added, the acid reacts with baking soda to release CO₂. A strong base or acid would be unsafe for food. So mild edible acid is correct.
Q23. Acidic nature of a substance is due to:
The acidic nature of a substance is due to the presence of hydrogen ions (H⁺) or hydronium ions (H₃O⁺) in aqueous solution. OH⁻ ions are responsible for basic nature, Cl⁻ and Na⁺ are specific ions. So H⁺ ions is correct.
Q24. When water is added back to anhydrous copper sulphate, the blue colour:
Anhydrous copper sulphate (CuSO₄) is white. When water is added, it becomes hydrated copper sulphate (CuSO₄·5H₂O) and the blue colour reappears. This is a test for the presence of water. So reappears is correct.
Q25. Strong acid shows:
Strong acids completely dissociate in water, producing a high concentration of H⁺ ions. They have low pH values (near 0). Weak acids produce fewer H⁺ ions. So more H⁺ concentration is correct.
Q26. Tartaric acid is added to baking soda in baking powder to:
Tartaric acid is added to baking soda in baking powder to neutralise the bitter taste of sodium carbonate (formed when baking soda decomposes). This prevents the food from tasting bitter. It does not slow the reaction, reduce gas, or make it acidic. So prevent bitter taste is correct.
Q27. The common name of CaOCl₂ is:
CaOCl₂ (calcium oxychloride) is the chemical formula of bleaching powder. Plaster of Paris is CaSO₄·½H₂O, baking soda is NaHCO₃, washing soda is Na₂CO₃·10H₂O. So bleaching powder is correct.
Q28. Mixing acid with water is:
Mixing a concentrated acid with water releases a large amount of heat. This is an exothermic reaction. That is why acid should be added to water slowly and with stirring. It is not reversible, endothermic (absorbs heat), or neutral. So exothermic is correct.
Q29. Egg-shell reacts with acid to give CO₂, hence acid present is:
Egg-shell contains calcium carbonate (CaCO₃). When it reacts with hydrochloric acid (HCl), it produces CO₂ gas: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. LiCl, NaCl, and KCl are salts, not acids. So HCl is correct.
Q30. Acid reacting with metal produces:
When an acid reacts with a metal, it produces a salt and hydrogen gas. For example: Zn + 2HCl → ZnCl₂ + H₂↑. Oxide and water is from metallic oxide + acid, base and hydrogen is not typical, salt and water is neutralisation. So salt and hydrogen is correct.
Q31. A neutral solution has pH:
A neutral solution has pH = 7. Pure water has pH 7. pH less than 7 is acidic, pH greater than 7 is basic. So 7 is correct.
Q32. Copper sulphate crystals appear blue because of:
Copper sulphate crystals (CuSO₄·5H₂O) appear blue because of the water of crystallisation present in the crystal. The water molecules are associated with the copper ions, giving the blue colour. When heated, they lose water and become white. So water of crystallisation is correct.
Q33. Acid-base indicators are:
Acid-base indicators are dyes (coloured substances) that change colour in acidic or basic media. Examples include litmus, phenolphthalein, and methyl orange. They are not acids, metals, or salts (though some indicators may be organic compounds). So dyes is correct.
Q34. Acids do not show acidic behaviour without water because:
Acids show acidic behaviour only in aqueous solution because water is needed to dissociate acids into H⁺ ions. Without water, acids do not produce ions and do not show acidic properties (like turning litmus, reacting with metals). So ions are absent is correct.
Q35. The formula of hydrated copper sulphate is:
Hydrated copper sulphate (blue vitriol) has the formula CuSO₄·5H₂O. It contains 5 molecules of water of crystallisation. CuSO₄·2H₂O is not common, CuSO₄ is anhydrous, CuSO₄·10H₂O is not correct. So CuSO₄·5H₂O is correct.
Q36. Fresh milk has pH 6; as it turns into curd, pH:
Fresh milk has pH around 6 (slightly acidic). When milk turns into curd, bacteria produce lactic acid, which increases the acidity. This means the pH decreases (becomes more acidic). So decreases is correct.
Q37. Plaster of Paris should be stored in moisture-proof container because:
Plaster of Paris reacts with moisture (water) to form gypsum, which hardens. If stored in a moisture-proof container, it remains usable. It does not melt, react with air, or evaporate. So it reacts with moisture is correct.
Q38. Heating copper sulphate removes:
On heating copper sulphate crystals, the water of crystallisation is removed, and the blue crystals become white anhydrous copper sulphate. Oxygen, copper, and sulphate are not removed. So water of crystallisation is correct.
Q39. Bleaching powder is prepared using:
Bleaching powder (CaOCl₂) is prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]. The reaction is: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. Quick lime (CaO) is used to make slaked lime, limestone (CaCO₃) is a raw material for quick lime. So slaked lime is correct.
Q40. The medicine used for indigestion is:
Indigestion is often caused by excess stomach acid. Antacids (like milk of magnesia, baking soda) are used to neutralise the excess acid and provide relief. Antibiotics treat infections, antiseptics prevent infection, analgesics relieve pain. So antacid is correct.
Q41. The sodium compound used for softening hard water is:
Washing soda (Na₂CO₃·10H₂O) is used to soften hard water. It removes calcium and magnesium ions (which cause hardness) by precipitating them as carbonates. Baking soda, sodium chloride, and sodium hydroxide are not used for this purpose. So washing soda is correct.
Q42. Basic nature of a substance is due to:
The basic nature of a substance is due to the presence of hydroxide ions (OH⁻) in aqueous solution. H⁺ ions are responsible for acidic nature, Na⁺ and Cl⁻ are specific ions. So OH⁻ ions is correct.
Q43. A basic solution has pH:
Basic solutions have pH greater than 7. pH less than 7 is acidic, pH equal to 7 is neutral. So more than 7 is correct.
Q44. The term 10H₂O in Na₂CO₃·10H₂O represents:
In Na₂CO₃·10H₂O (washing soda), the 10H₂O represents the water of crystallisation — a fixed number of water molecules chemically bonded to each formula unit of sodium carbonate. It is not wet salt, dissolved water, or free water. So water of crystallisation is correct.
Q45. Plaster of Paris is used for:
Plaster of Paris has multiple uses: in hospitals for supporting fractured bones (as casts), for decorative purposes (statues, mouldings), and for making toys and other articles. So all of these is correct.
Q46. Gypsum has the chemical formula:
Gypsum is calcium sulphate dihydrate with the formula CaSO₄·2H₂O. CaCO₃ is calcium carbonate, CaSO₄·½H₂O is Plaster of Paris, CaSO₄ is anhydrous calcium sulphate. So CaSO₄·2H₂O is correct.
Q47. The pH scale ranges from:
The pH scale ranges from 0 (most acidic) to 14 (most basic). 7 is neutral. So the correct range is 0 to 14.
Q48. When sodium hydrogen carbonate solution is heated, it forms:
On heating sodium hydrogen carbonate (NaHCO₃), it decomposes to form sodium carbonate (Na₂CO₃), carbon dioxide (CO₂), and water (H₂O). The reaction is: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O. Sodium chloride, sodium hydroxide, and sodium sulphate are not formed. So sodium carbonate is correct.
Q49. On heating sodium hydrogen carbonate, it decomposes to form:
This is the same as