Match the following and choose the correct option.

(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

The correct answer is option 2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii).

When pH of rainwater is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water but is corroded when the pH in the mouth is below 5.5.

Stinging hair of nettle leaves inject methanoic acid causing burning pain. pH of methanoic acid is approx. 3.47.

Our body works within the pH range of 7.0 to 7.8. pH of Blood is 7.4.