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Q1. The acidic nature of acids is due to the presence of:
Acids show acidic nature because they produce hydrogen ions (H⁺) when dissolved in water. For example, HCl → H⁺ + Cl⁻. The H⁺ ions are responsible for the sour taste, reaction with metals, and turning blue litmus red. Chloride, sulphate, and oxygen ions do not cause acidity. So hydrogen ions is correct.
Q2. Adding water to concentrated acid is dangerous because:
Adding water to concentrated acid is dangerous because the reaction is highly exothermic — it releases a large amount of heat. The heat can cause the acid to splash violently, leading to burns and injuries. The correct and safe method is to add acid to water slowly while stirring. So heat may cause splashing is correct.
Q3. Curd should not be stored in copper vessels because:
Curd contains lactic acid, which is acidic in nature. When stored in copper vessels, the acid reacts with copper to form toxic copper salts. This can make the curd poisonous and harmful to health. It does not become sweet, copper does not melt, and rusting is for iron. So acid reacts with copper is correct.
Q4. Hydrogen ions are represented correctly as:
Hydrogen ions in aqueous solution are represented as H⁺(aq) to show they are in water. In water, H⁺ ions combine with water molecules to form hydronium ions (H₃O⁺), but H⁺(aq) is the correct representation for hydrogen ions in solution. H₂ is hydrogen gas, H₃ is not a stable ion, and H⁺ alone is used in equations but (aq) adds context. So H⁺(aq) is correct.
Q5. Which oxide is acidic?
Carbon dioxide (CO₂) is an acidic oxide. It reacts with bases to form salt and water: CO₂ + 2NaOH → Na₂CO₃ + H₂O. CuO, MgO, and Na₂O are all basic oxides (metallic oxides). So CO₂ is correct.
Q6. Which substance conducts electricity in aqueous solution?
Acids conduct electricity in aqueous solution because they dissociate into ions (H⁺ and anions). These ions carry electric current. Alcohol, glucose, and oil do not dissociate into ions and do not conduct electricity. So acid is correct.
Q7. Carbon dioxide is classified as a:
CO₂ is a non-metallic oxide and is acidic in nature. It reacts with bases to form salt and water. Metallic oxides are basic, and neutral oxides (like CO, NO) do not show acidic or basic properties. So acidic oxide is correct.
Q8. The reaction of acid with base always results in:
The reaction between an acid and a base is called neutralisation. It always produces a salt and water. For example: NaOH + HCl → NaCl + H₂O. Precipitate may or may not form, gas is not always formed, and heat is often released but not the only product. So salt and water is correct.
Q9. Alkalis are described as:
Alkalis (soluble bases) are soapy to touch, bitter in taste, and corrosive in nature. They turn red litmus blue. They are not sweet, safe, weak, harmless, or neutral. So soapy, bitter and corrosive is correct.
Q10. Dry HCl gas does not show acidic nature because:
Dry HCl gas does not show acidic nature because it does not produce hydrogen ions (H⁺) in the absence of water. Acids only show their acidic properties when dissolved in water, where they dissociate to give H⁺ ions. HCl gas itself is not a base or neutral — it just lacks ions. So hydrogen ions are absent is correct.
Q11. Effervescence during reaction of a compound with acid indicates formation of:
Effervescence (bubbling) during the reaction of a compound with acid indicates the release of a gas. For metal carbonates and bicarbonates, the gas released is carbon dioxide (CO₂). Hydrogen gas is released when metals react with acids, but effervescence in the context of compounds (like carbonates) indicates CO₂. So carbon dioxide is correct.
Q12. Dilution results in:
Dilution is the process of adding water to a solution, which decreases the concentration of ions per unit volume. The number of ions remains the same, but they become more spread out. So decrease in ion concentration is correct.
Q13. While diluting an acid, the acid should be added to:
When diluting a concentrated acid, the acid should always be added slowly to water (not water to acid). This is because the reaction is highly exothermic, and adding water to acid can cause violent splashing. Adding acid to water allows the heat to be absorbed safely. So water is correct.
Q14. Non-metallic oxides generally react with:
Non-metallic oxides are acidic in nature. They react with bases to form salt and water. For example: CO₂ + 2NaOH → Na₂CO₃ + H₂O. They do not generally react with acids, metals, or salts. So bases is correct.
Q15. Lime water is a solution of:
Lime water is a dilute solution of calcium hydroxide [Ca(OH)₂] in water. It is used to test for CO₂. Calcium carbonate is limestone, calcium chloride is a salt, calcium oxide is quick lime. So calcium hydroxide is correct.
Q16. Which solution does NOT show acidic behaviour?
Alcohol (like ethanol) is not an acid — it is neutral. It does not produce H⁺ ions in solution, so it does not show acidic behaviour. H₂SO₄, nitric acid, and HCl are all acids. So alcohol solution is correct.
Q17. The gas evolved when calcium carbonate reacts with acid is tested using:
When calcium carbonate reacts with acid, carbon dioxide gas is evolved. Carbon dioxide is tested by passing it through lime water, which turns milky. Phenolphthalein and litmus are acid-base indicators, not tests for CO₂. So lime water is correct.
Q18. Sodium hydroxide in water produces:
Sodium hydroxide (NaOH) dissociates in water to give sodium ions (Na⁺) and hydroxide ions (OH⁻): NaOH → Na⁺ + OH⁻. These OH⁻ ions are responsible for the basic nature. So Na⁺ and OH⁻ is correct.
Q19. HCl shows acidic character only in:
HCl shows acidic character only when dissolved in water (aqueous solution). In the dry or gaseous state, HCl does not produce H⁺ ions and therefore does not show acidic properties. So aqueous solution is correct.
Q20. The cation responsible for acidic properties is:
The cation (positively charged ion) responsible for acidic properties is H⁺ (hydrogen ion). Cl⁻ is an anion, Na⁺ is a cation of a base, OH⁻ is the anion responsible for basic properties. So H⁺ is correct.
Q21. The process of reducing concentration of acid or base is called:
Dilution is the process of adding water to an acid or base to reduce its concentration. Reduction is gain of electrons, neutralisation is acid-base reaction, oxidation is loss of electrons. So dilution is correct.
Q22. Carbon dioxide reacts with calcium hydroxide to form:
Carbon dioxide reacts with calcium hydroxide (lime water) to form calcium carbonate and water: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Calcium carbonate is the white precipitate that makes lime water milky. So calcium carbonate and water is correct.
Q23. The reaction of a non-metallic oxide with a base shows that non-metallic oxides are:
Non-metallic oxides react with bases to form salt and water, which shows they are acidic in nature. For example: CO₂ + 2NaOH → Na₂CO₃ + H₂O. Metallic oxides are basic. So acidic is correct.
Q24. Hydrogen ions cannot exist independently because they:
Hydrogen ions (H⁺) cannot exist independently in aqueous solution because they combine with water molecules to form hydronium ions (H₃O⁺). This is because H⁺ has no electrons and is highly reactive. So combine with water is correct.
Q25. Concentrated sulphuric acid should be handled with care because it:
Concentrated sulphuric acid should be handled with care because its dilution with water is highly exothermic — it releases a large amount of heat. This can cause splashing and burns. It is not weak, does not freeze easily, and is not neutral. So is highly exothermic in water is correct.
Q26. Which compound produces H₃O⁺ ions in water?
HCl is an acid. When dissolved in water, it produces H⁺ ions which combine with water to form hydronium ions (H₃O⁺): HCl + H₂O → H₃O⁺ + Cl⁻. NaOH and KOH produce OH⁻ ions (bases), and CaO is a basic oxide. So HCl is correct.
Q27. Which of the following is an alkali?
An alkali is a base that dissolves in water. Sodium hydroxide (NaOH) is soluble in water and is therefore an alkali. Zinc oxide, copper oxide, and magnesium oxide are metallic oxides (bases) but are insoluble in water, so they are not alkalis. So sodium hydroxide is correct.
Q28. Which ion is common to all bases?
All bases produce hydroxide ions (OH⁻) in water. This is the ion common to all bases. H⁺ is common to acids, Cl⁻ is specific to chlorides, Na⁺ is specific to sodium compounds. So OH⁻ is correct.
Q29. Bases generate which ion in water?
Bases generate hydroxide ions (OH⁻) in water. For example: NaOH → Na⁺ + OH⁻. H⁺ is from acids, Cl⁻ from chlorides, CO₃²⁻ from carbonates. So OH⁻ is correct.
Q30. The products of neutralisation reaction are:
Neutralisation is the reaction between an acid and a base. The products are always a salt and water. For example: HCl + NaOH → NaCl + H₂O. Salt and hydrogen is from acid + metal, acid and base are reactants. So salt and water is correct.
Q31. H⁺ ions react with OH⁻ ions to form:
H⁺ ions (from acids) and OH⁻ ions (from bases) combine to form water (H₂O): H⁺ + OH⁻ → H₂O. This is the essence of neutralisation. Acid, salt, and hydrogen are not formed in this reaction. So water is correct.
Q32. All acids show similar chemical properties because they produce:
All acids show similar chemical properties because they produce H⁺ ions in aqueous solution. This common ion is responsible for their acidic nature. OH⁻ is for bases, Na⁺ and Cl⁻ are specific ions. So H⁺ ions is correct.
Q33. The bulb glows only in acid solution because:
The bulb glows in an acid solution because acids dissociate into ions (H⁺ and anions) in water. These ions carry electric current, completing the circuit. Liquids alone do not conduct, colour does not cause conduction, and heat is not the reason. So acids produce ions is correct.
Q34. Calcium carbonate reacts with hydrochloric acid to form calcium chloride, water and:
Calcium carbonate (CaCO₃) reacts with hydrochloric acid (HCl) to form calcium chloride, water, and carbon dioxide: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. Hydrogen gas is from acid + metal, oxygen and nitrogen are not produced. So carbon dioxide is correct.
Q35. The glowing of a bulb in acid solution indicates:
The glowing of a bulb in an acid solution indicates that the solution conducts electricity, meaning electric current is flowing through it. This happens because of the presence of ions. It does not indicate gas evolution, heat production, or neutralisation directly. So flow of electric current is correct.
Q36. Neutralisation reaction involves:
A neutralisation reaction is specifically the reaction between an acid and a base. The products are salt and water. Metal + salt, base + metal, and acid + metal are different types of reactions. So acid + base is correct.
Q37. Hydrogen gas is identified by:
Hydrogen gas is identified by the characteristic ‘pop’ sound when a burning splint is brought near it. Pungent smell is for gases like ammonia, yellow flame is not specific, turning lime water milky is for CO₂. So pop sound on burning is correct.
Q38. If a gas extinguishes a burning candle, the gas is likely to be:
Carbon dioxide is a non-supporter of combustion — it extinguishes a burning candle. Oxygen supports combustion (makes flame brighter), hydrogen burns with a pop, nitrogen is inert but does not extinguish as effectively. So carbon dioxide is correct.
Q39. Hydrogen ions exist in aqueous solution as:
Hydrogen ions (H⁺) cannot exist independently in water. They combine with water molecules to form hydronium ions (H₃O⁺). This is the true form in which H⁺ exists in aqueous solution. H₂O₂ is hydrogen peroxide, H₂ is hydrogen gas, H⁺ alone is not stable. So H₃O⁺ is correct.
Q40. Bases that dissolve in water are called:
Bases that dissolve in water are called alkalis. For example, NaOH and KOH are alkalis. Insoluble bases like CuO and Fe₂O₃ are not alkalis. Salts, acids, and oxides are different categories. So alkalis is correct.
Q41. Which ion is common to all acids?
The ion common to all acids is H⁺ (hydrogen ion). OH⁻ is common to bases, Na⁺ is specific to sodium compounds, Cl⁻ is specific to chlorides. So H⁺ is correct.
Q42. Which of the following solutions conducts electricity?
Hydrochloric acid solution conducts electricity because it dissociates into H⁺ and Cl⁻ ions. Sugar, glucose, and alcohol solutions do not dissociate into ions and do not conduct electricity. So hydrochloric acid solution is correct.
Q43. Acids react with metals to form:
Acids react with metals to produce a salt and hydrogen gas. For example: Zn + 2HCl → ZnCl₂ + H₂↑. Metal oxide and water is from metallic oxide + acid, base and hydrogen is not a general reaction, salt and oxygen is incorrect. So salt and hydrogen is correct.
Q44. Dissolving an acid in water is a:
Dissolving an acid in water is an exothermic process — it releases a large amount of heat. This is why acid should be added to water slowly, not vice versa. It is not neutral, not reversible in the sense of a chemical change, and not endothermic. So exothermic process is correct.
Q45. Sour substances corrode metal vessels because they are:
Sour substances like curd, lemon juice, and vinegar contain acids. These acids react with metals (like copper, aluminium) to corrode them. This is why sour substances should not be stored in metal vessels. So acidic is correct.
Q46. Which reaction explains acidic nature of CO₂?
The acidic nature of CO₂ is shown by its reaction with a base (NaOH) to form salt and water: CO₂ + 2NaOH → Na₂CO₃ + H₂O. CO₂ + Ca(OH)₂ is the lime water test (also shows acidic nature), but CO₂ + NaOH is a general reaction with a base. Among the options, CO₂ + NaOH directly shows acidic oxide + base → salt + water. So CO₂ + NaOH is correct.
Q47. The gas usually liberated when an acid reacts with a metal is:
When an acid reacts with a metal, hydrogen gas is usually liberated. For example: Mg + 2HCl → MgCl₂ + H₂↑. Carbon dioxide is from carbonates, nitrogen is not produced, oxygen is not produced. So hydrogen is correct.
Q48. Which base forms OH⁻ ions in water?
NaOH (sodium hydroxide) is a base that dissociates in water to form Na⁺ and OH⁻ ions: NaOH → Na⁺ + OH⁻. HCl and H₂SO₄ are acids (produce H⁺), CO₂ is an acidic oxide. So NaOH is correct.
Q49. Electric current in acid solutions is carried by:
Electric current in acid solutions is carried by ions (H⁺ and anions). The movement of these charged particles constitutes the electric current. Atoms and molecules are neutral and do not carry current. So ions is correct.
Q50. Glucose and alcohol solutions do not conduct electricity because they:
Glucose and alcohol solutions do not conduct electricity because they do not dissociate into ions. They remain as neutral molecules in solution. They are not acids (though some are weak), they are not solids in solution, and they do dissolve. So do not form ions is correct.