The resistance of a conductor varies inversely as

The correct answer is B. Area of cross-section.

The resistance of a conductor is inversely proportional to its area of cross-section. This means that if the area of cross-section is doubled, the resistance will be halved. This is because the resistance of a conductor is due to the collisions of electrons with the atoms in the conductor. The more electrons there are in a given volume, the more collisions there will be, and the higher the resistance will be. The area of cross-section is a measure of the volume of a conductor, so it is directly proportional to the number of electrons in the conductor.

The other options are incorrect.

• Option A: Length. The resistance of a conductor is directly proportional to its length. This means that if the length of a conductor is doubled, the resistance will also be doubled. This is because the longer the conductor, the more electrons have to travel, and the more collisions they will have with the atoms in the conductor.
• Option C: Temperature. The resistance of a conductor is generally increased by increasing the temperature. This is because the electrons in a conductor have more energy at higher temperatures, and they are therefore more likely to collide with the atoms in the conductor.
• Option D: Resistivity. Resistivity is a measure of the resistance of a material per unit length and unit area. It is a property of the material, and it does not change with the length or area of the conductor.