Which of the following is the unit used to measure time?

• A. Hour (h)
• B. Second (s)
• C. Minute (min)
• D. Week (wk)

Answer: (B)

Time is measured with a standard unit that stays constant across contexts. In science, that standard is the second, the SI base unit for time. A second is defined by a precise number of vibrations of a cesium-133 atom, which gives a highly reproducible tick. Because of this, seconds provide a universal, exact basis for calculating durations and rates. The other options are common everyday units, but they are built from seconds: a minute is 60 seconds, an hour is 3600 seconds, and a week is seven days (each day composed of 24 hours, and so on). So while those units are convenient for daily use, the fundamental unit used to measure time is the second.