Which of the following is not a unit of time

Light year is distance travelled by a light ray through vacuum in 1 year, it's a notion of distance not time.

A light year is not a unit of time; rather, it is a unit of distance. It represents the distance that light travels in one year, which is approximately 9.46 trillion kilometers (or about 5.88 trillion miles).

The other options are related to time:

• Microsecond is a unit of time, equal to one millionth of a second.
• Leap year refers to a year that has one extra day (366 days instead of the usual 365) to keep the calendar year synchronized with the astronomical year.
• Lunar month is the time it takes for the moon to complete one orbit around the Earth, which is roughly 29.5 days.

Therefore, while microsecond, leap year, and lunar month are all units that measure time, a light year is a unit of distance.