Question: Which of the following is not the unit of time? [PMT/NEET-1991]
a. Micro second
b. Leap year
c. Lunar months
d. Parallactic second

Answer: d. Parallactic second

Solution: Microsecond, leap year, and lunar month measure time, whereas “parallactic second” (arcsecond of parallax) is an angle used in astronomy, not time.