Which determines the state of matter for any material?
a. the size of the atoms
b. the hardness of the material
c. the behavior of the molecules
d. the weight of the material

I think the answer is c) the behaviour of molecules is the closest.
i learnt that particle movement and attraction within matter determine whether it is solid, liquid, or gas.
so if it's gas, the particles within it are spread apart and are moving randomly, whereas in a solid, they have strong forces of attraction between the particles and so they stay in a rigid lattice :)

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.