To which group and period of the modern periodic table do ‘X’ with electronic configuration 2,8,6 belong? State its valency.  

Solution: From the electronic configuration given above, we see that element X has 6 valence electrons in the outermost shell. So the group number of element X in the periodic table is

$$6+10=16$$

From the above configuration it can be seen that three electron shells are present in the atom of element X. So the period number of element X is 3. This means that, X belongs to the 3rd period of the periodic table. 

Since X has a tendency to accept 2 electrons to attain noble gas configuration, therefore, the valency of X is 2.