If a sample contains 21.2 g n, how many moles of n does it contain?

To calculate the number of moles of a substance, divide the amount of substance with the molar mass. The molar mass of nitrogen is approximately 14 grams per mole. Divide the given 21.2 g of N with the molar mass. The division will give an answer of 1.514 moles. Thus, there are approximately 1.514 moles of nitrogen in the sample. 

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.