Question

Which of the following is a physical change ? a) Melting of butter b) Burning of paper c) Rusting of iron d) Changing of wheat into bread 2. Milk turning sour is a chemical change ? a) Physical change b) Chemical change c) Reversible change d) None of these"

Answer 1

A physical change is when the form of a substance is altered, but it does not transform into another. The melting of butter is an example of this. Chemical changes, however, involve a substance transforming into new substances. An example is when milk turns sour, resulting from a process in which milk's lactose is converted into lactic acid by bacteria.

In the context of scientific terminology, a physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. Looking at the provided options, a) Melting of butter is an example of a physical change. This is because while the butter changes from a solid to a liquid state, it still remains butter. It's a reversible process and the molecular composition remains unaltered.

On the other hand, a chemical change occurs when a substance is transformed into one or more new substances. Such changes are often not easily reversed. In the case of Milk turning sour, it is a chemical change. It is a process in which bacteria convert lactose in the milk into lactic acid, changing the composition and hence, the properties of the milk.

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