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Physical and Chemical Changes — Science STD 7 — Question

Gujarat BoardEnglish MediumSTD 7SciencePhysical and Chemical Changes1 Mark
MCQ
Which of the following statements is not correct?
  • A
    In a chemical change, color of the object may change.
  • ✓
    In a chemical change, heat will always be released.
  • C
    A chemical change always involves a physical change.
  • D
    Rusting of iron becomes faster when humidity is high.
✓

Answer

Correct option: B.
In a chemical change, heat will always be released.
Signs of a chemical reaction include unexpected color change.
When copper reacts with the elements, it turns from its element color of reddish$-$brown to green.
So it is a chemical change.
Heat may or may not be released in a chemical reaction. It depends on the type of reaction.
Chemical changes cause a substance to change into an entire substance with a new chemical formula.
So its shape, size, etc also changes.
For rusting, the presence of both oxygen and water is essential.
The content of moisture in the air is high, which means if it is more humid, rusting becomes faster.

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