Answer:
Light travels faster in a less dense medium
Step-by-step explanation:
In a less dense medium, light will travel faster than it did in the more dense medium (an example of this transition can be light going from water to air).
This is because in a less dense medium there ares less particles, so light finds less resistence in its path.
The opposite happens in a more dense medium, there are more particles so light will travel slower because more particles will get in the way.
In summary, the more dense the medium, the more particles it has, and the slower that light will travel in it.