The molar mass of i2 is 253.80 g/mol, and the molar mass of ni3 is 394.71 g/mol. how many moles of i2 will form 3.58 g of ni3?

The balanced chemical reaction is:

N2 +3 I2 = 2NI3

We are given the amount of product formed. This will be the starting point of our calculations.

3.58 g NI3 ( 1 mol NI3 / 394.71 g NI3 ) ( 3 mol I2 / 2 mol NI3 ) = 0.014 mol I2.

Thus, 0.014 mol of I2 is needed to form the given amount of NI3.

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. 

You would do 1500/4 and the answer is 375