What determinate quantity is adopted as a standard of measurement?

• A. Constant
• B. Unit
• C. Scale
• D. Magnitude

Answer: (B)

The main idea is that measurement relies on a fixed reference quantity known as a unit. A unit is a precisely defined magnitude used to express measurements, like a meter for length or a kilogram for mass, providing a standard so all quantities can be compared consistently. A constant is a fixed value used in equations, not the general standard for measuring different quantities. A scale describes the markings or range of an instrument, but not the fundamental standard itself. Magnitude refers to the size of a quantity, which is what you measure, not the standard you measure with. So the determinate quantity adopted as the standard of measurement is a unit.