Displacement reaction
- CBSE · NCERT Class 10, Ch 1 Chemical Reactions and Equations
In a displacement reaction, a more reactive element pushes a less reactive element out of its compound and takes its place.
A metal can only push out a metal that is less reactive than itself. So you need to know which of the two is more reactive. The reactivity series gives that order.
In a double displacement reaction, two compounds swap their ions. If a product is a solid that does not dissolve, it is called a precipitate.
A small example
Put an iron nail in blue copper sulphate solution: Fe + CuSO₄ → FeSO₄ + Cu. Iron is more reactive than copper, so it takes copper's place. The nail gets a brown coat of copper, and the blue colour fades. Count the atoms: 1 Fe, 1 Cu, 1 S and 4 O on each side.
Where marks go
Question 29 of CBSE's 2026-27 Science sample paper claims iron filings turn magnesium sulphate solution green. The 2026-27 Science marking scheme gives 1 mark for saying the claim is wrong, with the reason. Iron is less reactive than magnesium, so it cannot push magnesium out.
The scheme's answer gives the reason, not only the verdict. It names which metal is more reactive. Read how to write answers for full marks.
Sources
Facts last checked against these sources on 30 September 2026.
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