Final answer:
The inertia of a body depends solely on its mass, which is the total quantity of matter within the object. The more massive an object is, the greater its inertia.
Step-by-step explanation:
The inertia of a body depends on the total quantity of matter that the body contains, which is its mass. Inertia is a property of matter that describes the tendency of an object to resist changes in its state of motion. Hence, it is only mass that affects the inertia of an object, not its density, volume, or shape. The more massive an object is, the greater its inertia and the more force it takes to change its state of motion.
For instance, it takes more force to push a truck than to push a bicycle because the truck has more mass, regardless of their densities or shapes. However, variables such as density and volume are important for other physical properties like buoyancy and pressure.