7. Of the balanced chemical equations below, which one most correctly represents a combustion reaction?
a. CaO + H20 Ca(OH) 2
b. CH4 + 202 CO2 + 2H2O
c. 2 Mg + O202 Mgo
d. 2 N2 + 3H22 NH 3

B. CH4 + 2O2 —> CO2 + 2H2O
Combustion reactions produce carbon dioxide and water by reacting a hydrocarbon with oxygen.

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. 

The air is going to come out because of the low pressure.