(a) What are amphoteric oxides? (b) Categorise the following based on their nature: $\mathrm{ZnO,Na_2O,CO_2}$

Q: (a) What are amphoteric oxides? (b) Categorise the following based on their nature: $\mathrm{ZnO,Na_2O,CO_2}$

**(a) Amphoteric oxides:** Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Aluminium oxide ($\mathrm{Al_2O_3}$) reacts with acids as well as bases: $$\mathrm{Al_2O_3(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2O(l)}$$ $$\mathrm{Al_2O_3(s) + 2NaOH(aq) \rightarrow 2NaAlO_2(aq) + H_2O(l)}$$ **(b) Categorisation:** - **Amphoteric oxide:** $\mathrm{ZnO}$ (zinc oxide) — the chapter names zinc oxide, along with aluminium oxide, as showing both acidic and basic behaviour. - **Basic oxide:** $\mathrm{Na_2O}$ (sodium oxide) — a metal oxide; it dissolves in water to form an alkali, $\mathrm{Na_2O(s) + H_2O(l) \rightarrow 2NaOH(aq)}$. - **Acidic oxide:** $\mathrm{CO_2}$ (carbon dioxide) — a non-metal oxide; as stated in the chapter, most non-metals produce acidic oxides when dissolved in water.

Metals and Non-metals

Amphoteric oxides

Official Answer

(a) Amphoteric oxides: Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Aluminium oxide ( $\mathrm{Al_2O_3}$ ) reacts with acids as well as bases:

$\mathrm{Al_2O_3(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2O(l)}$

$\mathrm{Al_2O_3(s) + 2NaOH(aq) \rightarrow 2NaAlO_2(aq) + H_2O(l)}$

(b) Categorisation:

Amphoteric oxide: $\mathrm{ZnO}$ (zinc oxide) — the chapter names zinc oxide, along with aluminium oxide, as showing both acidic and basic behaviour.
Basic oxide: $\mathrm{Na_2O}$ (sodium oxide) — a metal oxide; it dissolves in water to form an alkali, $\mathrm{Na_2O(s) + H_2O(l) \rightarrow 2NaOH(aq)}$ .
Acidic oxide: $\mathrm{CO_2}$ (carbon dioxide) — a non-metal oxide; as stated in the chapter, most non-metals produce acidic oxides when dissolved in water.

Hint

Recall the exact two metal oxides the NCERT text names as amphoteric, and remember non-metal oxides are generally acidic while metal oxides are generally basic.

Analysis & Explanation

The definition and examples are directly grounded in Section 3.2.1: "Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides," with the text naming aluminium oxide and zinc oxide as the two examples. The chapter also states "most non-metals produce acidic oxides when dissolve in water. On the other hand, most metals, give rise to basic oxides," which justifies classifying $\mathrm{CO_2}$ as acidic and $\mathrm{Na_2O}$ as basic. $\mathrm{ZnO}$ is explicitly grouped with $\mathrm{Al_2O_3}$ as amphoteric, showing dual acid-base behaviour, unlike the purely basic $\mathrm{Na_2O}$ or purely acidic $\mathrm{CO_2}$ .

Common Mistakes

1Classifying ZnO as simply 'basic' because it is a metal oxide, forgetting the chapter explicitly calls out ZnO as amphoteric alongside Al2O3.
2Forgetting to write balanced equations showing reaction with both an acid and a base when defining amphoteric oxides.
3Misclassifying CO2 as neutral instead of acidic — the chapter says most non-metal oxides are acidic, and CO2 forms carbonic acid in water.

Interesting Facts

Amphoteric oxides are used in this dual behaviour to purify aluminium ore (bauxite) in the Bayer process, where Al2O3 dissolves in NaOH while impurities like Fe2O3 (a basic oxide) do not.

Zinc oxide's amphoteric nature is why it can react away in both acidic and alkaline environments, a property exploited in sunscreen and paint formulations.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2026?

This question carries 2 marks in the CBSE Class 10 Science 2026 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Amphoteric oxides" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2026 paper?

This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2026 paper.