What quantity measures the amount of matter in an object?
volume
temperature
mass
density

Mass

Explanation:

Every object present in the earth occupies some space and a definite mass. This is known as the matter.  The matter has 3 states - solid, liquid, and gas. The three types of matter occupy some space, hence they have a definite volume. The different matters have a density also. The density is the packing of the materials like solid objects are more tightly packed than the liquid and gases. The quantity of all the materials is measured by the mass. It means how heavy the object is known as the mass. By measuring the mass of an object one can measure the quantity of a matter.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

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