BECE Science 2026 Paper

Concept:A natural acid is an acid formed by living organisms or by natural fermentation, and it has a $\text{pH}$ below $7$.Explanation:Vinegar is produced when bacteria ferment sugars into ethanoic acid, $\mathrm{CH_3COOH}$, which is a natural acid.This acid gives vinegar a $\text{pH}$ below $7$, which confirms that vinegar is acidic.Wood ash is alkaline because it contains basic carbonates and oxides that raise its $\text{pH}$ above $7$.Saliva is nearly neutral, with a $\text{pH}$ between $6.7$ and $7.3$, and it does not contain a natural acid group.Bile is an alkaline digestive fluid with a $\text{pH}$ between $7.6$ and $8.6$, so it cannot be classified as acidic.Among the four options, only vinegar is acidic and contains a natural acid, ethanoic acid.Answer:A. Vinegar.