Question

The elements A, B and C have the following electronic configuration :
A =2,7
B=2,8,5
C=2,8,8
Write the positions of these elements in the periodic table

Answer 1

Answer:

1)B

2)A

3)B

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Answer 2

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In this case, the number of valence electron is more than 2.

So, Group number =Number of valence electron +10

Now,

The element A has 7 valence electrons.

$\therefore$Group number =7+10=17

It has two occupied electronic shells.

$\therefore$Period =2nd

Similarly, for the element B,

Group number =5+10=15

It has three occupied electronic shells.

$\therefore$Period =3rd

For element C,

Group number =8+10=18

It has three occupied electronic shells.

$\therefore \:$Period =3rd