Science — AI-generated practice question

(i) Tooth Decay after eating sugar-rich food:
Bacteria in the mouth break down sugars to produce acids. When the pH of the mouth falls below 5.5, the acid corrodes tooth enamel (calcium hydroxyapatite), causing tooth decay. Using basic toothpastes neutralises the excess acid and helps prevent decay.

(ii) Farmers treat acidic soil with slaked lime:
Plants require a specific pH range for healthy growth. If soil is too acidic (low pH), farmers add slaked lime — calcium hydroxide, Ca(OH)₂ — which is basic. It neutralises the excess acid, raising the soil pH to a suitable level for crop growth.

(iii) Bee-sting pain relieved by baking soda:
A bee-sting injects an acid into the skin, causing pain and irritation. Baking soda (sodium hydrogen carbonate) is a mild base. Applying it on the stung area neutralises the acid, providing relief from pain.

(iv) Acid rain is harmful to aquatic life:
When pH of rainwater falls below 5.6, it is called acid rain. When it flows into rivers, it lowers the pH of river water. Living organisms can survive only within a narrow pH range; the lowered pH makes survival of aquatic life difficult or impossible.

(v) Stomach uses HCl; antacids provide relief:
The stomach produces HCl, which helps in digestion of food. During indigestion, excess acid is produced, causing pain and irritation. Antacids are mild bases (e.g., milk of magnesia — Mg(OH)₂) that neutralise the excess acid, restoring normal pH and giving relief.

Source: Chapter 2 — Acids, Bases and Salts; Section 2.3.1 Importance of pH in Everyday Life

---

• The question asks for any FOUR out of five, but all five are answered here — in an exam, choose four and write them. Each point should be roughly equal in length (~25 words).
• Each point must mention pH explicitly and link it to the concept of neutralisation or pH range — that's what the examiner looks for.
• Key terms to use: "neutralise," "pH falls below," "narrow pH range," "mild base/acid," "corrodes."
• Avoid writing generic statements; each answer must name the acid/base involved and state the effect on pH.