Answer : Yes, distance measurements based on the speed of light used for objects in space.
Explanation : A light year is measurement of distance that light travel in a one year.
In a one year light travels 9460000000000 kilometer.
We know that, speed of light is 
and time is 31536000 seconds in 1 year
so, distance = speed of light X time
Now, the light year is 
Example : The nearest star to earth is about 4.3 light year away.
Use formula for Echo which is Velocity=2(Distance)/time so 343=2(150)/T 343T=300..T=300/343=0.9 seconds
Answer:
Option B
Explanation:
According to quantum theory of radiation electromagnetic field or electromagnetic radiation( like light) produce by accelerated charge object and the quantum of EM radiations is photon which has discrete energy. So, EM field can have only certain values of total energy and no other value due the discrete nature of the energy of photon. Hence option B is correct
