Which statement best compares pure substances to mixtures? Pure substances contain small amounts of impurities. Mixtures contain large amounts of
impurities.
Pure substances must be made of two chemical materials. Mixtures can be made of only one
chemical material.
Pure substances are either compounds or elements. Mixtures are homogeneous or
heterogeneous combinations.
Pure substances are liquids dissolved in liquids or gases dissolved in gases. Mixtures are
gases dissolved in liquids or solids dissolved in liquids.

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. 

Perimeter? wheres the answers