Question

Identify the group number of the element having its electronic configuration: $1s^2$$2s^2$ $2p^6$$3s^2$$3p^6$ $3d^5$$4s^2$

• A. 8
• B. 7
• C. 17
• D. 5

Answer 1

The correct option is B 7

The electronic configuration given is $1s^2$ $2s^2$ $2p^6$ $3s^2$$3p^6$$3d^5$ $4s^2$
Here the last electron is in the $d$ - subshell and therefore the element is from the $d$ - block.

In $d$ - block:
Group number =
Number of electrons in the $ns$ subshell + Number of electrons in the $(n-1)d$ subshell

$\therefore GroupNumber=2+5=7$