Answer the following. (i) Write one example each of one metal that is so soft that it can be cut with a knife, and one non-metal that is a good conductor of electricity. (ii) Using the electronic configuration, explain how Mg atom combines with oxygen to form magnesium oxide by transfer of electrons. [Atomic number : Mg = 12, O = 8]

ScienceCBSE Class 10 · Board exam 2026, set 31/2/1 · 3 marks · Short answer

CBSE Class 10 Science 2026: question 26(a)

Set in the CBSE Class 10 board exam of 2026, paper 31/2/1, section B, question 26(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26(a) · 3 marks · Short answerMetals and Non-metals

Answer the following.

(i)
Write one example each of one metal that is so soft that it can be cut with a knife, and one non-metal that is a good conductor of electricity.
1 mark
(ii)
Using the electronic configuration, explain how Mg atom combines with oxygen to form magnesium oxide by transfer of electrons. [Atomic number : Mg = 12, O = 8]
2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/2/1.

Hints

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

Hint 1

Alkali metals are very soft; one allotrope of carbon conducts electricity.

Hint 2

Write 2,8,2 for Mg and 2,6 for O. How many electrons must each lose or gain to get an octet?

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.

(i) Soft metal that can be cut with a knife: sodium (or lithium or potassium).
½ mark
(i) Non-metal that is a good conductor of electricity: graphite (a form of carbon).
½ mark
(ii) Mg (Z = 12) has configuration 2, 8, 2. It loses its 2 valence electrons to form $M g^{2 +}$ (2, 8): $M g \to M g^{2 +} + 2 e^{-}$
½ mark
O (Z = 8) has configuration 2, 6. It gains these 2 electrons to form $O^{2 -}$ (2, 8): $O + 2 e^{-} \to O^{2 -}$
½ mark
Electron-dot representation: $M g :$ (2 dots) $+ \ddot{.. O}$ (6 dots) $\to [M g]^{2 +} [: \ddot{.. O} :]^{2 -}$ . Arrows show the two electrons moving from Mg to O.
½ mark
The oppositely charged ions $M g^{2 +}$ and $O^{2 -}$ are held by strong electrostatic attraction, forming ionic magnesium oxide $M g O$ . Both ions now have a stable octet.
½ mark

Answer: (i) Sodium (or Li/K); graphite. (ii) Mg (2,8,2) loses 2e⁻ → Mg²⁺; O (2,6) gains 2e⁻ → O²⁻; Mg²⁺O²⁻ forms ionic MgO.

Where the marks are

Soft metal example: Na/K/Li (½ mark)
Graphite (½ mark)
Electronic configurations and formation of Mg²⁺ (½ mark)
Formation of O²⁻ (½ mark)
Electron transfer shown by electron-dot diagram (½ mark)
Ionic bond in Mg²⁺O²⁻ (½ mark)

Revise the chapter

Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)
Topic: Ionic Compounds: Formation and Properties

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/2/1: every question, by section.

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CBSE Class 10 Science 2026: question 26(a)

Hints

Step-by-step solution

Revise the chapter

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