If the Atomic No of the Element Is 16 so its electronic configuration is 2,8,6 so it has 3 shells or orbits so it belongs to period 3 bcoz of having 3 shells then its valence shell [Last shell] has 6 electrons so it belongs to group IV - A (which is now called Group 16) hope u Understand. if any doubts or problems regarding to dis plz consult me