The correct answer is C. 100 %.
The resistivity of aluminium is 2.65 x 10-8 ohm-metres, while the resistivity of copper is 1.68 x 10-8 ohm-metres. This means that for the same electrical resistance, an aluminium conductor will need to be 1.65 times thicker than a copper conductor. However, aluminium is only about 60% the density of copper, so the aluminium conductor will only weigh about 100% as much as the copper conductor.
Option A is incorrect because the weight of an aluminium conductor is not 50% of the weight of a copper conductor of identical cross-section.
Option B is incorrect because the weight of an aluminium conductor is not 60% of the weight of a copper conductor of identical cross-section.
Option D is incorrect because the weight of an aluminium conductor is not 150% of the weight of a copper conductor of identical cross-section.