Science — AI-generated practice question

(a) A universal indicator is a mixture of several indicators that shows different colours at different concentrations of hydrogen ions, allowing us to measure the pH of a solution (scale 0–14). A single indicator like litmus only tells us whether a substance is acidic or basic (turns red or blue) — it cannot tell how strong the acid or base is. The universal indicator gives a range of colours, enabling quantitative measurement of H⁺ ion concentration.

(b) Procedure: Take about 2 g of backyard soil in a test tube, add 5 mL water, shake well, filter, and collect the filtrate. Test the filtrate with universal indicator paper and note the colour to find the approximate pH.

Conclusion: We can determine whether the soil is acidic, neutral, or alkaline, and find out the ideal pH range required for healthy growth of plants in that region. If soil pH is very low (acidic), a farmer may treat it with lime to neutralise excess acid.

(c) Our body performs all metabolic activities within a pH range of 7.0 to 7.8. Living organisms can survive only within a narrow pH range. If the pH goes beyond this range — due to disease, diet, or acid rain entering water bodies — enzyme activity is disrupted and cells cannot function normally, making survival difficult.

Source: Chapter 2, Section 2.3 and 2.3.1

---

• (a): Examiners want the key phrase "mixture of several indicators" and the contrast that litmus is qualitative (acid/base only) while universal indicator is quantitative (gives pH value).
• (b): Follow Activity 2.12 steps precisely. The conclusion must mention "ideal soil pH for plant growth" — that's the exact line the textbook uses. Bonus: linking low pH to lime treatment (from the Questions section) shows application.
• (c): Stick to the textbook line about "narrow range of pH change" and metabolic activity. Don't over-explain — two to three crisp sentences are enough for the marks available.