Which one of the following is a chemical change?

[amp_mcq option1=”Dissolving sugar in water” option2=”Melting of ice” option3=”Crystallization” option4=”Milk turning sour” correct=”option4″]

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UPSC NDA-1 – 2022

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A chemical change involves the formation of new substances with different chemical properties. Milk turning sour is a process where lactose is converted into lactic acid by bacteria, resulting in a change in chemical composition.

Physical changes alter the form or appearance of a substance but not its chemical identity (e.g., dissolving, melting, freezing, boiling, crystallization). Chemical changes result in the formation of one or more new substances with different chemical properties (e.g., burning, rusting, cooking, souring of milk).

Dissolving sugar in water, melting of ice, and crystallization are all physical changes. In milk turning sour, bacteria perform fermentation, converting lactose (a sugar) into lactic acid, which changes the taste and properties of the milk. This is a clear example of a chemical reaction producing new substances.

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