Step 1: Understanding the Concept
Group 16 is the chalcogen family: O, S, Se, Te, Po.
Step 2: Check the options
S, Te and Po are all members of group 16.
At (astatine) lies in group 17, the halogens.
Step 3: Compare the options
So astatine does not belong to group 16, which is option (D).
Final Answer:
Astatine is not in group 16.
\[ \boxed{\text{(D) }\text{At}} \]