The correct answer is A. 0.4 ohm.
The resistance of a wire is proportional to its length and inversely proportional to its cross-sectional area. If the length of a wire is doubled, its resistance will also be doubled. However, if the cross-sectional area of the wire is doubled, its resistance will be halved.
In this case, the length of the wire is doubled, but the cross-sectional area is not changed. Therefore, the resistance of the wire will be doubled, from 0.2 ohm to 0.4 ohm.
Option B is incorrect because the resistance of the wire is not doubled when the length is doubled.
Option C is incorrect because the resistance of the wire is not halved when the length is doubled.
Option D is incorrect because the resistance of the wire is not unchanged when the length is doubled.