Question

which statement correctly compares the speed of light?
the speed of light through space is much greater than 3 x 10^8 m/s.
the speed of light in glass is much greater than 3 x 10^8 m/s.
the speed of light in glass is faster than the speed of light through space.
the speed of light in glass is slower than the speed of light through space.

Explanation:

The speed of light in a vacuum (space) is approximately $3\times10^{8}$ m/s. When light enters a medium like glass, it interacts with the atoms in the glass, causing it to slow down. So the speed of light in glass is slower than in space.

Answer:

The speed of light in glass is slower than the speed of light through space.