Concept:
The inductive reactance (impedance due to an inductor) is
\[
X_L=\omega L.
\]
For a long solenoid,
\[
L=\mu_0 n^2Al,
\]
where
\[
n=\text{number of turns per unit length}.
\]
Hence,
\[
L\propto n^2.
\]
Since
\[
X_L=\omega L,
\]
for the same frequency,
\[
X_L\propto n^2.
\]
Step 1: Write the given ratio.
\[
n_1:n_2=2:1.
\]
Step 2: Find the ratio of inductances.
\[
L_1:L_2
=
n_1^2:n_2^2.
\]
\[
=
2^2:1^2.
\]
\[
=
4:1.
\]
Step 3: Find the ratio of impedances.
Since
\[
X_L\propto L,
\]
\[
X_{L1}:X_{L2}
=
4:1.
\]
Therefore,
\[
\boxed{\frac{X_{L1}}{X_{L2}}=4}
\]
\[
\boxed{\text{Answer = (B)}}
\]