Write balanced chemical equation for the reactions that occur when (a) steam is passed over red hot iron. (b) natural gas is burnt in air. (c) glucose reacts with oxygen in the cells of our body and provides energy.

(a) 3Fe + 4H_2O → Fe_3O_4 + 4H_2; (b) CH_4 + 2O_2 → CO_2 + 2H_2O; (c) C_6H12O_6 + 6O_2 → 6CO_2 + 6H_2O + energy

ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 3 marks · Short answer

CBSE Class 10 Science 2025: question 27

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerChemical Reactions and Equations

Write balanced chemical equation for the reactions that occur when

(a)
steam is passed over red hot iron.
0 marks
(b)
natural gas is burnt in air.
0 marks
(c)
glucose reacts with oxygen in the cells of our body and provides energy.
0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Iron reacts with steam to give a mixed oxide, $F e_{3} O_{4}$ , and a gas.

Hint 2

Natural gas is mostly methane, and glucose oxidation is aerobic respiration. Balance C, then H, then O.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(a) $3Fe (s) + 4 H_{2} O (g) \to F e_{3} O_{4} (s) + 4 H_{2} (g)$
1 mark
(b) Natural gas is mainly methane: $C H_{4} (g) + 2 O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)$ + heat and light
1 mark
(c) $C_{6} H_{12} O_{6} (aq) + 6 O_{2} (g) \to 6C O_{2} (g) + 6 H_{2} O (l)$ + energy
1 mark

Answer: (a) $3 F e + 4 H_{2} O \to F e_{3} O_{4} + 4 H_{2}$ ; (b) $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ ; (c) $C_{6} H_{12} O_{6} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O$ + energy

Where the marks are

Balanced equation for iron with steam (1 mark)
Balanced equation for combustion of methane (1 mark)
Balanced equation for respiration of glucose (1 mark)

Revise the chapter

Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)
Topic: Balancing Chemical Equations

Practise this chapterBoard-style questions from Chemical Reactions and Equations, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/6/1: every question, by section.

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CBSE Class 10 Science 2025: question 27

Hints

Step-by-step solution

Revise the chapter

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