Chlorine can be prepared in the laboratory by the reaction of manganese dioxide with hydrochloric acid, HCl(aq), as described by the chemical equation
MnO,-) + 4 HCl(aq) → MnCl(aq) + 2 H2O(1) + Cl ()
How much MnO2(s) should be added excess HCl(aq) to obtain 245 mL Cl2 (g) at 25°C and 745 Torr?
mass of MnO2=?g

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. 

Ithink carbon dioxide, i am not completely sure.tell me if i am wrong.

Oxygen= 88ghydrogen= 12g