NCERT Question 11

Why are decomposition reactions called the opposite of combination reactions? Write equations.

Answer:

• Decomposition Reaction: One substance breaks down into two or more simpler substances.

  • Example:
    CaCO3 → heat^ CaO + CO2​

• Combination Reaction: Two or more substances combine to form a single product.

  • Example:
    CaO + CO₂ → CaCO₃​

They are opposites because decomposition splits a compound, while combination joins elements/compounds.