Question

Number of valence electrons present in an atom A belongs to 3rd group and 3rd period
is ....​

Answer 1

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As it is in period 3 valence shell is 3 that is n=3 and since it's present in group 2, it has 2 valence electrons in the third shell. Hence its valence shell configuration is 3s^2

Hence in the first orbital, it will have 2 whereas in second orbital it will have 8 electrons, on the whole, it has 12 electrons that is the atomic number is 12. Hence the name of the element is magnesium.

Answer 2

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As it is in period 3 valence shell is 3 that is n=3 and since it's present in group 2, it has 2 valence electrons in the third shell. Hence its valence shell configuration is . 

As it is in period 3 valence shell is 3 that is n=3 and since it's present in group 2, it has 2 valence electrons in the third shell. Hence its valence shell configuration is .  Hence in the first orbital, it will have 2 whereas in second orbital it will have 8 electrons, on the whole, it has 12 electrons that is the atomic number is 12. Hence the name of the element is magnesium.