Question

which of the following symbols would be included in the noble gas notation for an element that had valence electrons in the 5s subshell?
ar
kr
xe
rn

Explanation:

Noble gas notation uses the noble gas from the previous period. The 5s subshell is in the fifth period. The noble gas in the fourth period is Kr (Krypton). Ar is in the third period, Xe in the fifth (but we need the one from the previous period for the notation when starting to fill 5s), and Rn is in the sixth period.

Answer:

Kr