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The electronic… (Class 10 Science SQP 2025-26, Q29B)

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ScienceCBSE Class 10 · Sample paper, session 2025-26 · 5 marks · Case-based

CBSE Class 10 Science sample paper 2025-26: question 29(B)

From the official CBSE sample question paper for 2025-26, section B, question 29(B), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q29(B) · 5 marks · Case-basedCompetency-basedCarbon and its Compounds

The electronic structures of atoms P and Q are shown below. Based on the information given above, answer the following questions:

  1. (a)

    If P and Q combine to form a compound, what type of bond is formed between them?

    1 mark
  2. (b)

    Give the chemical formula of the compound formed.

    1 mark
  3. (c)

    The compound so formed is dissolved in water. Is the resultant solution acidic or basic in nature? Justify your answer.

    1 mark
  4. (d)

    Write the chemical equation for the reaction between 'Q' and ethanol.

    1 mark
  5. (e)

    What will be the formula of the compound formed when 'P' undergoes bonding with carbon?

    1 mark

Figure in the paper: Two Bohr-type atomic diagrams. Atom P: a nucleus with a shell of 2 electrons (dots at top) and an outer shell with 6 electrons... (electrons shown as dots on the orbits: two dots on the inner circle region, and the outer shell carries the remaining dots). Atom Q: nucleus with two shells, inner shell with 2 electrons and outer shell with 8 electrons arranged around the circle, and a third shell with 2 electrons at the bottom and top. Labels P and Q are written in the centres. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Count electrons in each shell to identify P and Q.

Hint 2

A metal giving electrons to a non-metal forms which kind of bond?

Hint 3

Use the valencies to write the formulas.

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.

  1. From the diagrams: P has configuration 2, 6, so it is oxygen (non-metal, needs 2 electrons). Q has one electron in its outermost (third) shell, configuration 2, 8, 1, so it is sodium (metal, loses 1 electron).

  2. (a) The metal Q transfers electrons to the non-metal P, so an ionic (electrovalent) bond is formed.

    1 mark

  3. (b) Q has valency 1 and P has valency 2, so the formula is **** (i.e. ).

    1 mark

  4. (c) Basic. is a metal oxide, and metallic oxides dissolve in water to form alkalis: .

    1 mark

  5. (d) (sodium ethoxide and hydrogen gas).

    1 mark

  6. (e) Carbon has valency 4 and P (oxygen) has valency 2, so the compound is **** ().

    1 mark

  7. For visually impaired students: (a) C–O: covalent bond; (b) Ca–O: ionic bond; (c) CaO conducts in the molten state because it has free ions; (d) CaO is a solid while is a gas; (e) valency of carbon in = 4.

Answer: (a) Ionic bond; (b) ; (c) Basic, metal oxide forms alkali; (d) ; (e)

Where the marks are

  • Ionic bond (1 mark)
  • Formula (1 mark)
  • Basic, with reason that metallic oxides are basic (1 mark)
  • Balanced equation of Q with ethanol (1 mark)
  • (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Carbon and its Compounds, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2025-26: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.