Please help me ASAP What is the main difference between the reaction in a hydrogen-oxygen fuel cell and the burning of hydrogen in the air?

A. When hydrogen burns in air, the oxidation and reduction reactions are separated.

B. The burning of hydrogen in air does not produce water.

C. The reaction in a fuel cell does not produce water.

D. The reaction in a fuel cell is very controlled.

If you open the bottle of perfume then nothing but the smell will come out of it and yes it is a type of gas smell because it’s say it in english so i can understand better and you

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. 

Sorry i dont understand the question can you rephase it?