What's mass? a. the sum of the number of protons and neutrons in an atom b. a measure of the amount of matter an object contains c. a measure of an element's attraction for electrons d. the force that gravity exerts upon an object

Mass is a measure of the amount of matter a substance contains.

B. A measure of the amount of matter an object contains

Explanation:

Mass is a measure of resistance which a body offers to its acceleration. Mass is a constant quantity and is the same in every part of the universe.

It also determines the attraction of an object to the gravitational force exerted by earth and other planets that have gravity.

Mass is not the same as weight which is the quantity that gives with which an object is attracted by gravity of a planet.