**Correct Option: C. Velocity** ### Detailed Explanation: To determine which of the given quantities is a vector, we first need to understand the difference between scalar and vector quantities: - **Scalar quantities** are those that have only magnitude (size) and no direction. Examples include temperature, mass, and energy. - **Vector quantities** have both magnitude and direction. Examples include velocity, force, and displacement. Now, let's analyze each option: **A. Temperature** - Temperature is a measure of the average kinetic energy of the particles in a substance. It is expressed in degrees (Celsius, Fahrenheit, Kelvin) and has no directional component. Therefore, temperature is a scalar quantity. **B. Mass** - Mass is a measure of the amount of matter in an object, typically measured in kilograms (kg). Like temperature, mass has only magnitude and no direction. Thus, mass is also a scalar quantity. **C. Velocity** - Velocity is defined as the rate of change of displacement with respect to time. It is expressed in units such as meters per second (m/s) and includes both a magnitude (how fast something is moving) and a direction (where it is moving towards). For example, saying "30 m/s to the north" indicates both speed and direction, making velocity a vector quantity. **D. Energy** - Energy is the capacity to do work and is measured in joules (J). It has magnitude but no direction. Therefore, energy is a scalar quantity. ### Why the Other Options are Wrong or Weaker: - **Temperature (A)**: As explained, it has no direction and is purely a measure of thermal energy. - **Mass (B)**: It is a fundamental property of matter that does not involve direction; it simply quantifies how much matter is present. - **Energy (D)**: While energy is crucial in physics, it does not have a directional component, making it a scalar. ### Summary of Key Concepts: 1. **Scalar vs. Vector**: Scalars have only magnitude; vectors have both magnitude and direction. 2. **Examples of Scalars**: Temperature, mass, and energy are all scalar quantities. 3. **Example of a Vector**: Velocity is a vector because it includes both speed and direction. 4. **Importance of Direction**: In physics, the direction of a vector can significantly affect the outcome of problems involving forces, motion, and other phenomena. ### Revision Summary: - Scalars have magnitude only; vectors have both magnitude and direction. - Temperature, mass, and energy are scalar quantities. - Velocity is a vector quantity because it includes direction. - Understanding the distinction between scalars and vectors is crucial for solving physics problems effectively.