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Q1. Tooth enamel is made up of:
Tooth enamel, the hardest substance in the human body, is made up of calcium phosphate (Ca₃(PO₄)₂) in the form of hydroxyapatite. It is this mineral that makes enamel strong. Calcium carbonate is found in limestone/marble, calcium oxide is quick lime, and calcium sulphate is gypsum. So calcium phosphate is correct.
Q2. A solution with pH greater than 7 is:
The pH scale ranges from 0 to 14. A pH of 7 is neutral (pure water). A pH less than 7 is acidic. A pH greater than 7 is basic (alkaline). Saline is not a pH category. So basic is correct.
Q3. Nettle sting is caused due to:
Nettle leaves have hair-like structures that inject methanoic acid (formic acid, HCOOH) when they sting. This causes a burning sensation and pain. Oxalic acid is in tomatoes, citric acid in citrus fruits, acetic acid in vinegar. So methanoic acid is correct.
Q4. Increasing pH value indicates:
The pH scale measures acidity or alkalinity. As pH increases from 0 to 14, the solution becomes less acidic and more basic (alkaline). So increasing pH indicates an increase in alkalinity. Increase in acidity would mean decreasing pH. So increase in alkalinity is correct.
Q5. Citric acid is found in:
Citric acid is found in citrus fruits like oranges, lemons, and grapefruits. Tomato contains oxalic and citric acid but is not the primary source. Sour milk contains lactic acid, and tamarind contains tartaric acid. So orange is correct.
Q6. Strong acids are those which produce:
Strong acids completely dissociate in water, producing a large number of H⁺ ions. For example, HCl → H⁺ + Cl⁻ (complete dissociation). Weak acids dissociate only partially and produce fewer H⁺ ions. So more H⁺ ions is correct.
Q7. Which planet has sulphuric acid clouds?
Venus has a thick atmosphere with clouds made of concentrated sulphuric acid (H₂SO₄). This makes the planet’s environment extremely acidic and hostile. Saturn, Jupiter, and Mars do not have sulphuric acid clouds. So Venus is correct.
Q8. Strong bases are those which produce:
Strong bases completely dissociate in water, producing a large number of OH⁻ ions. For example, NaOH → Na⁺ + OH⁻ (complete dissociation). Weak bases dissociate partially and produce fewer OH⁻ ions. So more OH⁻ ions is correct.
Q9. Solution A has pH 6 and solution B has pH 8. Higher H⁺ concentration is in:
The pH scale is logarithmic: lower pH means higher H⁺ concentration. pH 6 is more acidic than pH 8. So solution A (pH 6) has a higher concentration of H⁺ ions than solution B (pH 8). So solution A is correct.
Q10. Higher the hydronium ion concentration, the pH value is:
Hydronium ion (H₃O⁺) concentration is directly related to H⁺ concentration. Higher H⁺ (or H₃O⁺) concentration means the solution is more acidic, which gives a lower pH value. So lower is correct.
Q11. The acid present in the stomach is:
The stomach produces hydrochloric acid (HCl), which helps in digestion by creating an acidic environment for enzymes and killing bacteria. It does not contain nitric, sulphuric, or acetic acid. So hydrochloric acid is correct.
Q12. Toothpastes are generally:
Toothpastes are generally basic in nature. They neutralise the acids produced by bacteria in the mouth, which helps prevent tooth decay. They are not acidic (that would damage teeth), neutral, or saline. So basic is correct.
Q13. Concentrated acids carry warning signs because they are:
Concentrated acids are corrosive — they can cause severe burns to skin and damage to materials. This is why they carry warning signs (like the corrosive symbol). They are not weak, diluted, or neutral. So corrosive is correct.
Q14. Relief from bee sting is obtained by applying:
Bee sting injects methanoic acid (formic acid), which is acidic. Applying baking soda (a base) neutralises the acid and provides relief. Vinegar and lemon juice are acidic and would make it worse. Salt is not effective. So baking soda is correct.
Q15. Solution with pH 8 is:
pH 8 is greater than 7, so it is basic (alkaline). pH 7 is neutral. A strong acid would have a very low pH (close to 0). So basic is correct.
Q16. Milk of magnesia is:
Milk of magnesia is a suspension of magnesium hydroxide [Mg(OH)₂] in water. It is used as an antacid to neutralise excess stomach acid. Magnesium oxide is MgO, magnesium sulphate is Epsom salt, magnesium chloride is a salt. So magnesium hydroxide is correct.
Q17. Antacids are used to:
Antacids are bases (like milk of magnesia, baking soda) that neutralise excess acid in the stomach. This relieves acidity and heartburn. They do not form gas as a primary function, increase digestion directly, or increase acidity. So neutralise excess acid is correct.
Q18. A solution with pH value 7 is:
A pH of 7 is exactly neutral. Pure water has pH 7. Acidic solutions have pH less than 7, and basic/alkaline solutions have pH greater than 7. So neutral is correct.
Q19. Normal pH range of human body is:
The normal pH range of human body fluids (especially blood) is approximately 7.0 to 7.8 (closer to 7.35–7.45 for blood). This slightly basic range is essential for proper functioning of enzymes and cells. So 7.0–7.8 is correct.
Q20. On diluting an acid, the concentration of hydronium ions H₃O⁺:
Dilution means adding water to an acid. This increases the volume of the solution, so the concentration of hydronium ions (H₃O⁺) decreases. The number of ions remains the same, but they are more spread out. So decreases is correct.
Q21. Plants require a specific range of pH for:
Plants require a specific pH range (usually slightly acidic to neutral) for healthy growth. The pH affects the availability of nutrients in the soil. If the soil is too acidic or too basic, plants cannot absorb nutrients properly, affecting their overall growth. So healthy growth is correct.
Q22. Acid rain affects aquatic life by:
Acid rain lowers the pH of rivers, lakes, and other water bodies (makes them more acidic). This harms aquatic life because many fish and other organisms cannot survive in acidic conditions. It does not neutralise water, increase oxygen, or increase pH. So decreasing pH of river water is correct.
Q23. Bacteria produce acids in mouth by:
Bacteria in the mouth degrade sugar and food particles left on teeth. This produces acids (like lactic acid) that attack tooth enamel and cause decay. Photosynthesis, reacting with water, and respiration are not the mechanisms of acid production by mouth bacteria. So degrading sugar and food particles is correct.
Q24. The safest method of diluting acid is:
The safest way to dilute a concentrated acid is to add acid slowly to water with constant stirring. This allows the heat released to be absorbed by the large volume of water. Adding water to acid can cause violent splashing and burns. So adding acid to water is correct.
Q25. Acid rain has pH less than:
Normal rain has a pH of about 5.6 due to dissolved CO₂ forming carbonic acid. Rain is called acid rain when its pH falls below 5.6, usually due to dissolved oxides of sulphur and nitrogen (SO₂, NO₂) forming stronger acids. So pH less than 5.6 is correct.
Q26. Tartaric acid is found in:
Tartaric acid is found in tamarind (imli) and grapes. Oranges and lemons contain citric acid, vinegar contains acetic acid. So tamarind is correct.
Q27. Excess acid in the stomach causes:
Excess acid in the stomach causes acidity, leading to irritation, heartburn, and pain in the stomach. This is relieved by antacids. It does not cause alkalinity (that would be excess base), neutrality, or improved digestion. So irritation and pain is correct.
Q28. Acidic nature of curd is due to:
Curd (yoghurt) is acidic because it contains lactic acid, produced by the fermentation of milk sugar (lactose) by bacteria. Oxalic acid is in tomatoes, citric acid in citrus fruits, acetic acid in vinegar. So lactic acid is correct.
Q29. Universal indicator paper is used because it:
Universal indicator paper (or solution) changes to different colours at different pH values. By comparing the colour with a pH chart, we can get a numerical pH value (0–14). It does not give heat, taste, or smell. So gives numerical pH value is correct.
Q30. The letter ‘p’ in pH stands for:
The ‘p’ in pH stands for ‘potenz’ (a German word meaning power). pH is a measure of the concentration of hydrogen ions, expressed as the negative logarithm of H⁺ concentration. While it is often interpreted as ‘power of hydrogen’, the original German term is potenz. So potenz is correct.
Q31. Dock plant is effective against nettle sting because it is:
Nettle sting injects methanoic acid (acidic). Dock plant contains a basic substance that neutralises the acid, providing relief. This is similar to applying baking soda. So basic is correct.
Q32. Lactic acid is found in:
Lactic acid is produced in curd (yoghurt) by bacterial fermentation of lactose. Vinegar contains acetic acid, lemon contains citric acid, tamarind contains tartaric acid. So curd is correct.
Q33. A solution with pH less than 7 is:
pH less than 7 indicates an acidic solution. pH 7 is neutral, and pH greater than 7 is basic (alkaline). So acidic is correct.
Q34. Oxalic acid is found in:
Oxalic acid is found in tomatoes and spinach. Lemon and orange contain citric acid, curd contains lactic acid. So tomato is correct.
Q35. While diluting an acid, acid is added to water because:
Diluting an acid is highly exothermic — it releases a lot of heat. If water is added to acid, the heat can cause violent splashing and burns. Adding acid to water allows the heat to be absorbed safely. So heat produced may cause splashing is correct.
Q36. Universal indicator shows different colours due to:
Universal indicator changes colour at different pH values because the concentration of H⁺ (or H₃O⁺) ions changes. Different pH means different ion concentration, which causes the indicator to show different colours. Temperature, pressure, and solution colour are not the reasons. So ion concentration change is correct.
Q37. Bee sting causes pain because it injects:
Bee sting injects methanoic acid (formic acid), which causes pain and burning. Acetic acid is in vinegar, citric acid in citrus fruits, lactic acid in curd. So methanoic acid is correct.
Q38. 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.
Q39. Life can survive only in a:
Most living organisms can survive only within a narrow pH range (around 7 to 7.8 for humans). Extreme acidic or basic conditions are harmful to life. So narrow pH range is correct.
Q40. pH value helps us determine the:
The pH value indicates whether a solution is acidic, basic, or neutral, and also gives an idea of the strength (concentration of H⁺ or OH⁻ ions). It does not determine density, colour, or smell. So strength of acid or base is correct.
Q41. Dry HCl gas does not change the colour of dry litmus paper because:
Dry HCl gas does not dissociate into H⁺ and Cl⁻ ions because there is no water. Acids only show their acidic properties and change litmus colour when dissolved in water, where H⁺ ions are produced. HCl gas does contain hydrogen, but ions are not formed. So hydrogen ions are not produced without water is correct.
Q42. The pH scale is used to measure:
The pH scale is specifically used to measure the concentration of hydrogen ions (H⁺) or hydronium ions (H₃O⁺) in a solution. It does not measure mass, pressure, or temperature. So hydrogen ion concentration is correct.
Q43. When excess base is added to sodium hydroxide solution, concentration of OH⁻ ions:
Sodium hydroxide is already a base. Adding more base (NaOH) increases the number of OH⁻ ions in the solution. So the concentration of OH⁻ ions increases. It does not become zero, decrease, or remain unchanged. So increases is correct.
Q44. Farmers treat acidic soil with:
Acidic soil is treated with bases like quick lime (CaO) or slaked lime [Ca(OH)₂] to neutralise the acidity and make the soil suitable for plant growth. Ammonium chloride is acidic (used for alkaline soil), sulphuric acid is an acid, sodium chloride is neutral. So quick lime or slaked lime is correct.
Q45. Basic solutions also contain H⁺ ions because:
Even basic solutions contain a small number of H⁺ ions because water (which is present in aqueous solutions) ionises very slightly to produce H⁺ and OH⁻ ions: H₂O ⇌ H⁺ + OH⁻. Bases do not produce H⁺, acids may be present but not in basic solutions, and salts reacting is not the reason. So water ionises slightly is correct.
Q46. Tooth decay starts when mouth pH falls below:
Tooth enamel (calcium phosphate) starts to dissolve when the pH in the mouth falls below 5.5. This happens when bacteria produce acids from sugar. pH 7 is neutral, and below 5.5 is the critical level for decay. So 5.5 is correct.
Q47. Soil pH can be tested using:
Soil pH is best tested using universal indicator paper or a soil pH meter. Universal indicator gives a range of colours corresponding to different pH values. Litmus paper only tells if it is acidic or basic, not the exact pH. Phenolphthalein only tests for bases. So universal indicator is correct.
Q48. Acetic acid is found in:
Acetic acid (CH₃COOH) is the main component of vinegar (about 5-8%). Orange and lemon contain citric acid, curd contains lactic acid. So vinegar is correct.
Q49. Weak acids are those which produce:
Weak acids dissociate only partially in water, producing fewer H⁺ ions. For example, acetic acid (CH₃COOH) is a weak acid. Strong acids produce more H⁺ ions. So fewer H⁺ ions is correct.
Q50. Dilution of acid results in:
Dilution of an acid by adding water decreases the concentration of H⁺ (or H₃O⁺) ions per unit volume. The number of ions remains the same, but they become more spread out. It does not increase strength, cause neutralisation (that requires a base), or form gas. So decrease in ion concentration is correct.