Which is true? The net potential change around a closed circuit loop is zero. The net potential change counterclockwise around a closed circuit loop is positive. The net potential change clockwise around a closed circuit loop is positive.

The net potential change around a closed circuit loop is zero. This is absolutely true.

Explanation:

The net potential change around a closed circuit loop is zero because when a charge circulates around a close loop its potential energy changes because it moves round around the loop, but its net potential change is zero when it moves around a close loop.Because its initial and final positions are same.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.