Question: Light year is a unit of: [PMT/NEET-1989]
a. Time
b. Mass
c. Distance
d. Energy

Answer: c. Distance

Solution: Light-year is the distance light travels in one year in vacuum;

$1\ \text{ly} = c \times 1\ \text{yr} \approx 9.46\times10^{15}\ \text{m}$

so it is a unit of length, not time.