A) 7, 15
B) 5, 12
C) 9, 17
D) 3, 11
Correct Answer: D
Solution :
s-block elements contain either 1 or 2 electrons in their outer most shell. \[3=1\,{{s}^{2}},\,2{{s}^{1}}\] \[11=1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{1}}\] From the above electronic configuration, it is clear that elements having atomic number 3 and 11 belong to s-block. Since, both contains one electron in outer most shell, these belong to alkali metals.
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