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Question

The electronic configuration of an element is 1s2 2s2 2p6 3s2 3p4. The atomic number and the group number of element 'X' (which is just below the said element in the periodic table) respectively are:

A
24 & 6
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B
34 & 6
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C
24 & 16
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D
34 & 16
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Solution

The correct option is D 34 & 16
Electronic configuration of an element: 1s2 2s2 2p6 3s2 3p4. As last electron is in p-subshell, the element is from p-block.

In p-block:
Group number = Number of valence electrons + 10
= (2+4) + 10
= 6+10
= 16
Atomic number = Number of electrons in electronic configuration
= 2 + 2 + 6 + 2 +4
= 16 ( i.e. sulphur)
But an element 'X' is first below the above element. So, group number will be the same, i.e., 16th and atomic number = 16 + 18
= 34
So, X is Selenium (Se) with atomic number = 34
and group number = 16

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