In-text Questions — pH and Its Effects — Acids, Bases and Salts

1. 12 marksNCERT Cl-10 Science, In-text Qs after §2.3.1, Q1

   You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

   Hint. Remember the direction of the pH scale — a smaller pH number means a bigger H⁺ concentration, not a smaller one.

   Step 1 — Recall the relationship between pH and H⁺ concentration. A lower pH corresponds to a higher hydrogen ion concentration — the two move in opposite directions.

   Step 2 — Compare A (pH 6) and B (pH 8). Since 6 is lower than 8, solution A has the higher H⁺ ion concentration.

   Step 3 — Classify each solution. pH 6 is below 7, so solution A is (weakly) acidic. pH 8 is above 7, so solution B is (weakly) basic.

   ✦ Answer: Solution A has more hydrogen ion concentration. Solution A (pH 6) is acidic; solution B (pH 8) is basic.

   Where students slip. Assuming the higher pH number means more H⁺ ions, since 8 is a bigger number than 6 — pH works in reverse: lower pH means more H⁺, not less.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §2.3.1, Q2

   What effect does the concentration of H⁺(aq) ions have on the nature of the solution?

   Hint. Think of this as the general rule behind the specific comparison in the previous question.

   Step 1 — State the general relationship. The more H⁺(aq) ions a solution has, the more strongly acidic it is (and the lower its pH). The fewer H⁺(aq) ions present, the closer the solution is to neutral or basic.

   Step 2 — Frame it as a scale. High H⁺ concentration → strongly acidic; moderate H⁺ concentration → weakly acidic; balanced H⁺ and OH⁻ → neutral; low H⁺ (relative to OH⁻) → basic, and increasingly so as H⁺ drops further.

   ✦ Answer: The higher the concentration of H⁺(aq) ions in a solution, the more acidic (and lower the pH of) that solution is; a lower H⁺ concentration means the solution is less acidic, neutral, or basic.

   Where students slip. Describing this only as 'high H⁺ = acid, low H⁺ = base' without the sliding-scale idea — acidity/basicity is a matter of degree, tied continuously to how much H⁺ is present, not a simple on/off switch.

3. 32 marksNCERT Cl-10 Science, In-text Qs after §2.3.1, Q3

   Do basic solutions also have H⁺(aq) ions? If yes, then why are these basic?

   Hint. It's never a question of H⁺ being completely absent — it's a question of which ion is in the majority.

   Step 1 — Answer the yes/no part. Yes — every aqueous solution, including basic ones, contains some H⁺(aq) ions, since water itself always produces a small amount of both H⁺ and OH⁻ ions.

   Step 2 — Explain why such a solution is still called basic. A solution is basic not because it has zero H⁺ ions, but because its concentration of OH⁻ ions is much greater than its concentration of H⁺ ions. It's this relative excess of OH⁻ over H⁺ that makes the solution behave as a base.

   ✦ Answer: Yes, basic solutions do contain some H⁺(aq) ions. They are basic because the concentration of OH⁻ ions in them greatly exceeds the concentration of H⁺ ions, not because H⁺ is completely absent.

   Where students slip. Answering 'no' — basic solutions are never completely free of H⁺ ions; the classification depends on which ion is present in far greater concentration.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §2.3.1, Q4

   Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

   Hint. All three named substances share one chemical property in common — think about what problem that property would fix.

   Step 1 — Identify what quicklime, slaked lime and chalk have in common. Calcium oxide, calcium hydroxide and calcium carbonate are all basic substances.

   Step 2 — Work out what problem a basic substance corrects in soil. Adding a basic substance to soil raises its pH, which is useful specifically when the soil is too acidic for the crop being grown.

   ✦ Answer: A farmer would use quicklime, slaked lime or chalk to treat soil that is too acidic, since all three are basic and neutralise the excess acidity, raising the soil's pH to a range suitable for healthy crop growth.

   Where students slip. Saying these substances are used for 'basic' soil — that's backwards; you add a base to fix soil that is already too acidic, not soil that is already basic.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc102.pdf) — five in-text question sets (19 questions total) plus one end-of-chapter Exercise (15 questions, not 20 as some older manifests claim). Bleaching powder is written as Ca(ClO)₂ in the current text, matching the chapter's own in-text question.. Questions are referenced from the NCERT textbook for identification.