Question

Light year is the unit of following physical quantity
A. Time
B. Distance
C. Mass
D. None

Answer 1

Distance is the measure of length or space between two objects or two points in free space.
Distances are generally measured in meters
There are several units used to measure the distances, namely meters, miles, inches, etc.

Complete step by step solution:
A light-year is a measure of distance. Which are light travels in one year.
Astronomers use this light-year measurement because it is very easy to compare numbers like $1$ and $100$ light-years than numbers like 5 billion miles and $674{\text{ }}trillion{\text{ }}miles$.
To understand how many miles there are in a light-year, you can look up the speed of light in miles per second and multiply by the number of seconds in a minute.
More recently the International Astronomical Union has stated that the year is the average Julian Year of $365.25$days or $31,557,600{\text{ }}seconds$. Here, the Light-Year having an exact value of ${\text{ }}9,460,730,472,580,800{\text{ }}metres.$
This distance is very large - and it is - but astronomically speaking a light-year isn’t even the distance to the next nearest star, which is Proxima Centauri some $4.24$ light-years away.
Finally, the light-year is the measure of distance.

Note:
A light-year is a measure of distance just like this Kilometer, meter and all.
A light-year is used to measure large distances like the distance of stars from us and other planets.
In one year light can travel $25,902,720,000 \times 365Km$. that is $9,454,492,800,000{\text{ }}Km$.