Which of the following is not the unit of time.

Parallactic second

The correct answer is Option (4) → Parallactic second

The unit of time among the given options is: Parallactic second

1. Microsecond: This is a unit of time equal to one millionth of a second (\(1 \mu s\)).

2. Leap year: While not a standard unit of time, a leap year is a calendar year containing one additional day added to keep the calendar year synchronized with the astronomical year.

3. Lunar month: This refers to the time it takes for the Moon to complete one orbit around the Earth, approximately 29.53 days

4. Parallactic second: This is not a recognized unit of time. Rather, it seems to be related to the concept of parallax in astronomy, which involves the apparent shift in position of an object when viewed from different perspectives.

Therefore, among the options given, "Parallactic second" is not a unit of time.