Question

which elements shows the same chemical properties.why?
the atomic numbers are 9,11,17

Answer 1

the elements with atomic numbers 9 and 17 show similar chemical properties because they have same valence shell electronic configuration i.e.., ns² np⁵
so they belong to the same group and we know that elements in the same group show similar chemical properites.

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Answer 2

9 and 17 atomic number elements show the same chemical properties.

Electronic configuration of 9: 2,7
Electronic configuration of 17: 2,8,7

Both the elements valence electrons are 7 that means they belong to the same group in the periodic table.

Therefore they show same chemical properties.