Step 1: Use Snell’s law.
According to Snell’s law,
\[
n_1\sin i=n_2\sin r
\]
where
\[
n_1=2,
\quad
n_2=1,
\quad
i=30^\circ
\]
Step 2: Substitute the values.
\[
2\sin30^\circ=1\cdot \sin r
\]
Since
\[
\sin30^\circ=\frac{1}{2},
\]
we get
\[
2\times \frac{1}{2}=\sin r
\]
\[
\sin r=1
\]
Step 3: Find the angle of refraction.
\[
r=90^\circ
\]
Step 4: Final conclusion.
Hence, the angle of refraction is
\[
\boxed{90^\circ}
\]