CBSE Class 10 Science 2019 Delhi Set 2

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Question : 3
Total: 9
Write the name, symbol and electronic configuration of an element X whose atomic number is 11.
OR
Can the following groups of elements be classified as Dobereiner's triad:
(a) Na,Si,Cl
(b) Be,Mg, Ca
Atomic mass of Be-9, Na-23, Mg-24, Si-28, Cl35,Ca40. Justify your answer in each case.
Solution:  
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