The correct option is ARGON.
To quickly find out the element that is been described by the electronic configuration, write down and add together all the index figures in the electronic configuration. The index figures in the above electronic configuration are 2, 2, 6, 2 and 6. If you add all these figures together, you will get 18 and the element that has the atomic number of 18 is argon.
We know that 
, where 
is density, 
is mass, and 
is volume.
Substitute in the values we know and solve:
What the definition of each period and group and element and every valence electron
