Which of the following measurement tools would you need to determine the
weight of an iPad?
A. graduated cylinder
B. double pan balance
C. scale
D. triple beam balance

It would be C.scale, because

A. is for liquid

B. is for measuring 2 things

and D. is for i don't know(lol)

but i think the scale would be the easiest way to measer an iPad

a electromagnetic waves

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.