Which one of the following correctly represents Sodium oxide? (A) Na^+2 2 [ × O × ]^-2 (electron-dot structure, as drawn) (B) 2 Na^+ [ ×× O× ]^-2 (electron-dot structure, as drawn) (C) 2 Na^+ 2 [ ×× O× ]^-1 (electron-dot structure, as drawn) (D) Na^+1 [ ×× O× ]^-2 (electron-dot structure, as drawn)

ScienceCBSE Class 10 · Sample paper, session 2023-24 · 1 mark · MCQ

CBSE Class 10 Science sample paper 2023-24: question 5

From the official CBSE sample question paper for 2023-24, section A, question 5, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q5 · 1 mark · MCQMetals and Non-metals

Which one of the following correctly represents Sodium oxide?

(A) $N a^{+ 2} 2 [\times O \times]^{- 2}$ (electron-dot structure, as drawn)
(B) $2 N a^{+} [\times \times O \times]^{- 2}$ (electron-dot structure, as drawn)
(C) $2 N a^{+} 2 [\times \times O \times]^{- 1}$ (electron-dot structure, as drawn)
(D) $N a^{+ 1} [\times \times O \times]^{- 2}$ (electron-dot structure, as drawn)

Figure in the paper: Four electron-dot (Lewis) structure options drawn as handwritten notation. Option a: Na with +2 charge, coefficient 2, oxide ion in brackets with -2 charge. Option b: 2Na+ with oxide ion in brackets with -2 charge. Option c: 2Na+ with coefficient 2 and oxide ion in brackets with -1 charge. Option d: Na with +1 charge and oxide ion in brackets with -2 charge. Each oxide ion is shown with 8 cross-marked electrons around O. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

How many electrons does sodium lose, and how many does oxygen gain?

Hint 2

Balance the total positive and negative charge.

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.

Na (2,8,1) loses 1 electron to form $N a^{+}$ . O (2,6) gains 2 electrons to form $O^{2 -}$ with an octet.
To balance the charge, two $N a^{+}$ ions combine with one $O^{2 -}$ ion, giving $N a_{2} O$ . This is written $2N a^{+} [O]^{2 -}$ , which is option (B).
1 mark

Answer: $2N a^{+} [O]^{2 -}$ , option (B)

Where the marks are

Selects the structure with two $N a^{+}$ ions and one oxide ion of charge $- 2$ (1 mark)

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Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)

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CBSE Class 10 Science sample paper 2023-24: question 5

Hints

Step-by-step solution

Revise the chapter

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