Which one of the following is a scalar quantity?

The correct option is Mass.

Step-by-Step Explanation:

In physics, physical quantities are categorized into two main types based on their properties: scalar quantities and vector quantities.

1. Scalar Quantity:
A scalar quantity is a physical quantity that has magnitude (size or numerical value) only, but no specific direction.
Examples include mass, distance, speed, time, energy, and temperature.

2. Vector Quantity:
A vector quantity is a physical quantity that has both magnitude and a specific direction, and follows the laws of vector addition.
Examples include weight, gravity (acceleration due to gravity), momentum, velocity, and force.

Analyzing the given options:

• Mass: It measures the amount of matter in an object. It only has magnitude (e.g., 5 kg) and does not point in any direction. Therefore, mass is a scalar quantity.

• Gravity (Acceleration due to gravity): It has both magnitude and acts vertically downward toward the center of the Earth. Therefore, it is a vector quantity.

• Momentum: It is defined as the product of mass and velocity ($p=mv$). Since velocity has direction, momentum also has both magnitude and direction, making it a vector quantity.

• Weight: Weight is the gravitational force acting on an object ($W=mg$). Since force acts in a specific direction (downward), weight is a vector quantity.

Thus, among the options provided, Mass is the only scalar quantity.