Naturally occurring magnesium has an atomic mass of 24.312 and consists of three isotopes. the major isotope is mg24, natural abundance 78.99%, relative atomic mass 23.98504. the next most abundant isotope is mg26, relative atomic mass 25.98259. the third most abundant isotope is mg25 whose natural abundance is in the ratio of 0.9083 to that of mg26. find the relative atomic mass of mg25.

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.