Question

What element forms an ion with an electronic configuration of 1s22s22p63s23p63d104s24p6 (or [kr]) and a −2 charge? Give the symbol for the element?

Answer 1

Answer :  The symbol of the element is Selenium (Se).

Explanation :  

Electronic configuration is distribution of electrons in an atom in                    atomic orbitals.

The electronic configuration of [Kr] =  $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}$

Total number of electrons in [Kr] = 36

Due to -2 charge, 2 electrons are withdrawn from the electronic configuration of [Kr].

Now the total number of electrons left = 36 - 2 = 34

And the Selenium[Se] is the element which has 34 number of electrons.

Electronic configuration of [Se] = $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{4}$