Which of the following is a physical change?
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Radioactive decay
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Photosynthesis
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Magnetising a needle
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Rusting of iron
C
Correct answer
Explanation
A physical change doesn't produce new substances and is often reversible. Magnetizing a needle only aligns magnetic domains - the material remains the same and can be demagnetized. Radioactive decay (A) changes elements, photosynthesis (B) produces glucose from CO₂ and water, and rusting (D) creates iron oxide - all are chemical changes.