Achemical change is a change in the of a substance.
a. composition
c. temperature
b. appearance
d. melting point

The answer should be composition because you are making a totally new substance when  you are changing it chemically. A physical change for example, would be cutting wood when in the end you still have wood. 

A chemical change is a change in the composition of a substance.

That is because it changes the bonds and how they form. 

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.