Final answer:
Mass is used to indicate the amount of matter an object contains because it is constant and independent of location, while weight varies with gravitational force.
Step-by-step explanation:
An object's mass is used to indicate the amount of matter it contains rather than its weight because mass is a measure of the amount of matter, and it remains constant regardless of the object's location.
In contrast, weight is the gravitational force acting on the mass of an object and thus depends on the local gravitational field strength, which can vary from place to place. Therefore, mass is a more reliable and universal measure of the quantity of matter.
Options b) and c) of your question are correct because weight depends on the gravitational field strength, which can vary with location, and mass remains constant regardless of location, while weight changes with it.
Option a) is also correct in a sense that mass is scalar and weight is vectorial, but it doesn't directly address the reason mass indicates the amount of matter. Option d) is incorrect because mass is not a measure of volume, and weight is not a measure of density; these are different physical properties.