Q1. [2] § 1.1 CHEMICAL EQUATIONS
When magnesium ribbon is burnt in air, an ash of white colour is produced. Write chemical equation for the reaction giving the chemical name of the ash produced. State the type of chemical reaction giving justification for your answer.
Previously asked in CBSE board exam
2024 31/3/1 Q21
Generated by claude-sonnet-4-6 · 2026-06-14 10:28 · grounding rag
Model Answer
Chemical equation:
$$2\text{Mg}(s) + \text{O}_2(g) \rightarrow 2\text{MgO}(s)$$
The white ash formed is magnesium oxide.
Type of reaction: It is a combination reaction because two reactants (magnesium and oxygen) combine to form a single product (magnesium oxide). It is also an oxidation reaction as magnesium gains oxygen.
Source: Chapter 1, Section 1.1; Chapter 3, Section 3.2.1
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Explanation
- The question asks for three things: the equation, the name of the ash, and the type of reaction with justification — address all three.
- The balanced equation must show 2Mg on the left to balance atoms (skeletal equation Mg + O₂ → MgO is unbalanced).
- Examiners accept combination reaction as the primary answer; mentioning oxidation as an additional point can fetch bonus credit or shows completeness.
- "Justification" means you must state why it is a combination reaction — always include the one-line reason.
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