The correct option is **C. Force**. ### Detailed Explanation 1. **Understanding Derived and Base Quantities**: - In the International System of Units (SI), quantities are classified into two categories: base quantities and derived quantities. - **Base quantities** are the fundamental physical quantities that are defined independently. They include: - Mass (kilogram, kg) - Length (meter, m) - Time (second, s) - **Derived quantities** are those that are derived from the base quantities through mathematical relationships. They are expressed in terms of the base quantities. 2. **Analyzing the Options**: - **A. Mass**: This is a base quantity. It is one of the fundamental measurements in physics and is measured in kilograms (kg). - **B. Length**: This is also a base quantity. It is measured in meters (m) and is fundamental to measuring distance. - **C. Force**: This is a derived quantity. Force is defined by Newton's second law of motion, which states that force equals mass times acceleration (F = ma). In SI units, force is measured in newtons (N), where 1 N = 1 kg·m/s². Thus, force is derived from the base quantities of mass (kg) and acceleration (m/s²). - **D. Time**: This is another base quantity. It is measured in seconds (s) and is fundamental to measuring duration. 3. **Why Other Options Are Incorrect**: - **A. Mass**: Incorrect because it is a base quantity, not derived. - **B. Length**: Incorrect for the same reason; it is a base quantity. - **D. Time**: Incorrect as it is also a base quantity. ### Formulas and Calculations - The formula for force is given by: \[ F = m \cdot a \] where: - \( F \) is the force in newtons (N), - \( m \) is the mass in kilograms (kg), - \( a \) is the acceleration in meters per second squared (m/s²). ### Common Pitfalls - Students often confuse derived quantities with base quantities. Remember that derived quantities are formed from combinations of base quantities. - It’s important to memorize the base quantities in the SI system to avoid confusion during exams. ### Revision Summary - **Base quantities** in SI include mass, length, and time. - **Derived quantities** are formed from base quantities; force is a prime example. - Force is calculated using the formula \( F = m \cdot a \). - Always differentiate between base and derived quantities to avoid mistakes in identification.