Electrons are able to travel close to speed of light.
When the light is traveling through vacuum.
Speed. All photons traveling through a vacuum travel at the speed of light.
ANY light traveling through the same medium (stuff) has the same speed.
Nobody knows for sure. We have never witnessed a physical object traveling faster than the speed of light.
Time required to do what? To move from one place to another, divide the distance by the speed of light.
The speed of light is determined by the electric and magnetic properties of the stuff it's traveling through. The "light" itself is just electrostatic and magnetic fields traveling together through the stuff. Change the electrical properties of the medium, and you change the speed of light through it.
That would depend on the medium which the light is traveling through.
is a constant, about 300,000,000 m/s.
When you (or an object) travel without changing speed, then you have constant velocity (speed). This means there is no change in speed (acceleration) when you (or an object) is traveling.
The speed of light is the result of the electrostatic and magnetic properties of the medium through which it's traveling. The speed changes only when those properties change.
When the speed of light in the two media is not the same.
It can approach the speed of light, but never actually hit it. The reason being that, from relativity, the mass of an object gets exponentially larger and larger as its velocity approaches the speed of light. At the speed of light, an objects mass would be infinite, which can't happen.As an aside, an object can go faster than light if both the object and the light are traveling through a media other than a vacuum. This is because light moves slower and slower through denser and denser materials. If the object has a charge, an effect called Cherenkov radiation occurs. This is light's equivalent to a sonic boom from sound. Measuring Cherenkov radiation was how physicists were able to show that neutrinos (the most abundant particles in the universe) have mass.