Question

Which of the following reactions is not a decomposition reaction?

• A. Starch is converted to glucose in our body
• B. Production of calcium oxide and carbon dioxide by calcium calcium carbonate
• C. Magnesium ribbon is burnt in air
• D. Electricity is passed through water

Answer 1

The correct option is C Magnesium ribbon is burnt in air

(A) Conversion of starch into glucose follow decomposition reaction because there is a breaking of a starch molecule into glucose.

(B) Calcium carbonate on heating breaks down into calcium oxide and carbon dioxide. Hence, it is a decomposition reaction.

(C) Magnesium ribbon when burnt in air, it gets oxidized to form magnesium oxide by a combination of magnesium and oxygen. Hence, it is the example of a combination reaction.

$2Mg+O_2\to 2MgO$

(D) Water gets ionized(breaks down) on passing electricity into $H^{+}$ and $O{H}^{-}$ ion. Hence, it is the example of the decomposition reaction.