In-text Questions — Oxidation and Combustion — Carbon and its Compounds

1. 12 marksNCERT Cl-10 Science, In-text Qs between §4.3 and §4.4, Q1

   Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

   Hint. Compare the -CH₂OH end of ethanol with the -COOH end of ethanoic acid — what has been added?

   Step 1 — Compare the two structures. Ethanol is CH₃-CH₂-OH; ethanoic acid is CH₃-COOH. The end carbon gains an extra oxygen atom in going from one to the other.

   Step 2 — Apply the definition of oxidation. Gaining oxygen during a reaction is the definition of oxidation used throughout this book, so converting ethanol to ethanoic acid — which adds oxygen to the molecule — is an oxidation reaction.

   Step 3 — Name what makes it happen. Oxidising agents such as alkaline potassium permanganate or acidified potassium dichromate supply this oxygen.

   ✦ Answer: Ethanol gains an oxygen atom in becoming ethanoic acid, and gaining oxygen is exactly what defines oxidation — carried out here using an oxidising agent like alkaline KMnO₄ or acidified K₂Cr₂O₇.

   Where students slip. Explaining this only in terms of 'ethanol turning into an acid' without connecting it back to the oxygen-gain definition of oxidation — the question specifically wants that link made explicit.

2. 22 marksNCERT Cl-10 Science, In-text Qs between §4.3 and §4.4, Q2

   A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

   Hint. Air is mostly nitrogen — think about what that means for how much oxygen actually reaches the flame.

   Step 1 — Recall what air is made of. Air is only about one-fifth oxygen, with most of the rest being nitrogen and other gases that don't support combustion.

   Step 2 — Compare burning in air versus pure oxygen. Burning ethyne in air would starve the flame of enough oxygen for complete combustion, giving a cooler, less efficient flame. Burning it in pure oxygen instead ensures complete combustion.

   Step 3 — Connect this to welding. Complete combustion in pure oxygen produces a much hotter flame than combustion in air would, and welding needs that very high temperature to melt metal.

   ✦ Answer: Air is only about 21% oxygen, so ethyne burnt in air doesn't get enough oxygen for complete combustion and produces a cooler flame; pure oxygen gives complete combustion and a much hotter flame, which is what welding requires.

   Where students slip. Saying air 'doesn't burn ethyne at all' — ethyne does burn in air, just less completely and at a lower temperature, which is exactly why it isn't hot enough for welding.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc104.pdf) — five in-text question sets (13 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (15 questions, not 20). Unchanged by rationalisation.. Questions are referenced from the NCERT textbook for identification.