What element has a noble gas notation (Xe) 6s2?
Barium has the noble gas configuration [Xe]6s².
You can learn about noble gas configurations at
To work backwards and find the element with a given configuration, you first find the noble gas in the Periodic Table.
Xe is element 54.
Your element has two more electrons (and two more protons) than Xe. It must be element 56. Look in the Periodic Table, and
Element 56 is barium, Ba.