A group of students floated a charged invisible tape above another charged tape. They determined that the approximate charge on the floating tape was about 6e^-09 C. The floating tape was 18 cm long and 1.25 cm wide. The ratio of the number of excess electronic charges to the number of molecules on the surface of the tape is the fraction of the molecules on the surface of the tape that have gained (or lost) an extra electronic charge e = 1.6x10^-19 C. What is this fraction? To estimate this, assume that molecules in the tape are arranged in a cubic lattice, as indicated in the accompanying figure, and that the diameter of a molecule in the tape is about 3x10^-10 m. Required:
What is the fraction of molecules with an extra charge?

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.

1 is a answer of a question

the correct answer is "inertia"