Step 1: Locate the element
Astatine has $Z = 85$. The noble gas radon (86) follows it.
Step 2: Reason
Because it sits just one place before radon, it is in group 17 with the halogens. Its valence shell is $6s^2 6p^5$.
Step 3: Reject others
Groups 16 and 18 end at Po and Rn, and group 1 is for alkali metals. So only 17 fits.
Final Answer:
Group 17, option (A).
\[ \boxed{17} \]