To express \( 8.21 \times 10^{-5} \) in the form \( __ \times 10^{-6} \), we can rewrite \( 10^{-5} \) as \( 10^{-6} \times 10^{1} \).
Thus, we have:
\[ 8.21 \times 10^{-5} = 8.21 \times 10^{-6} \times 10^{1} = 8.21 \times 10^{-6} \times 10 = 82.1 \times 10^{-6} \]
So, the answer is:
\[ 82.1 \times 10^{-6} \]