Which statement best explains why protons are used
to identify an element?

Every atom of an element will have the same number of protons

Explanation:

Protons are used to identify an element because every atom of an element will have the same number of protons.

Protons are the positively charged particles found in an atom. They are called the atomic numberEvery atom of an element has the same number of protons. An element can have different atom in form of isotopes. These isotopes are only identifiable by the number of protons they have.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.