Final answer:
The correct statement regarding the nature of physical changes in chemistry is A. Physical changes may be reversed by changing the temperature, as this does not alter the chemical composition of a substance.
Step-by-step explanation:
The question concerns the nature of physical changes and properties in chemistry. So, let's examine the statements provided to select the best one:
- A. Physical changes may be reversed by changing the temperature. This statement is true. An example would be the melting of ice into water, which can be reversed by lowering the temperature to freeze the water back into ice.
- B. Physical changes alter the composition of the substances involved. This is inaccurate. Physical changes do not alter the chemical composition of a substance; instead, they affect the form or physical properties, such as size, shape, or state.
- C. Physical properties are not valid characteristics for identifying a substance. This is false. Physical properties are often used to identify materials, such as melting point, density, and color.
- D. Physical properties are mostly extensive in nature. This statement is incorrect. Physical properties can be either extensive or intensive. Extensive properties depend on the amount of matter (like mass or volume), while intensive properties do not (like density or color).
- E. Physical changes are usually accompanied by chemical changes. This is not generally true. Physical changes can occur without any chemical changes, such as when water boils or ice melts.
Therefore, the correct statement is A. Physical changes may be reversed by changing the temperature.