Question

In which of the following reactions is a combination reaction taking place?
I. CuO + H$_2$ $\xrightarrow{\Delta}$ Cu + H$_2$O
II. ZnO + C → Zn + CO
III. 4Na + O$_2$ → 2Na$_2$O
IV. CH$_4$ + 2O$_2$ → CO$_2$ + 2H$_2$O

• A. Only III
• B. Only IV
• C. II and III
• D. I, III and IV

Hint:

In a combination reaction, two or more reactants combine to form a single product. Always look for reactions with a single compound formed on the right-hand side.

Answer 1

The Correct Option is A

We are asked to identify which of the given reactions is a combination reaction. A combination reaction is one in which two or more reactants combine to form a single product.

Let us analyze each reaction:

I. CuO + H₂ → Cu + H₂O
This is a reduction reaction, where CuO is reduced to Cu and hydrogen is oxidized to H₂O. Since it produces more than one product, it is not a combination reaction.

II. ZnO + C → Zn + CO
This is also a reduction reaction. Zinc oxide is reduced to zinc. Carbon is oxidized to carbon monoxide. It is not a combination reaction.

III. 4Na + O₂ → 2Na₂O
This is a classic example of a combination reaction, as sodium and oxygen combine to form a single compound: sodium oxide.

IV. CH₄ + 2O₂ → CO₂ + 2H₂O
This is a combustion reaction. It produces more than one product and hence is not a combination reaction.

Thus, only reaction III is a combination reaction.

Correct Answer: (A) Only III