CBSE Class 10 Science sample paper 2023-24: question 7
From the official CBSE sample question paper for 2023-24, section A, question 7, for 1 mark. Try it first; the hints and our step-by-step solution are below.
Q7 · 1 mark · MCQMetals and Non-metals
An element 'M' has 50% of the electrons filled in the 3rd shell as in the 2nd shell. The atomic number of 'M' is:
- (A)10
- (B)12
- (C)14
- (D)18
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 are there in a filled 2nd shell?
Hint 2
Take half of that number for the 3rd shell, then add up all the shells.
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.
The 2nd shell holds 8 electrons. 50% of 8 is 4, so the 3rd shell has 4 electrons.
- 1 mark
The configuration is 2,8,4, so the atomic number is . The answer is option (C).
Answer: 14, option (C)
Where the marks are
- Works out the configuration 2,8,4 and atomic number 14 (1 mark)
Revise the chapter
- Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)
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