Which of the following is not a physical quantity of measurement ?

Options

A. Length
B. Rust
C. Mass
D. Density

Answer

To determine which of the following is not a physical quantity of measurement, we will analyze each option provided:

1. **Length**: This is a fundamental physical quantity that measures the distance between two points. It can be quantified using units such as meters, centimeters, etc. Therefore, length is a physical quantity.

2. **Rust**: Rust is not a physical quantity; rather, it is a chemical substance formed through a chemical reaction (oxidation) when iron reacts with moisture and oxygen in the air. Since rusting involves a change in chemical composition, it does not represent a measurable physical quantity.

3. **Mass**: Mass is another fundamental physical quantity that measures the amount of matter in an object. It can be quantified in units such as kilograms or grams. Thus, mass is a physical quantity.

4. **Density**: Density is defined as mass per unit volume (Density = Mass/Volume). It is a derived physical quantity that describes how much mass is contained in a given volume of a substance. Therefore, density is also a physical quantity.

Based on this analysis, the option that is not a physical quantity of measurement is **Rust**.

### Final Answer:
**B. Rust**