Jacques charles described the direct relationship between temperature and volume of all gases at constant pressure. should this be called charles's law or charles's theory? explain.

This should be called as Charles law.

Law's are those which do not have any explanation or mechanism behind them, they are obtain by performing several experiments and then conclude to a one liner.

Since Jacques charles gives the relationship by performing number of experiment, there is no scientific explanation why it happens that's it should be known as  Charles law.

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.