How many oxygen atoms in 4 al 2 o 3

 The  number of oxygen   atoms  that are  in 4 Al₂O₃  are 12 atoms

Explanation

The subscript  in  a chemical formula indicate the  number  of atoms of element  immediately   before the subscript.coefficient  is the  number  in front  of  the formula  and tells  us how many molecules  of a given formula  are  present.Since 4Al₂O₃  has coefficient of 4   and the subscript   of O is 3 the number of O atoms =  4 x 3=12 atoms

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. 

That is a lot of moles that you have