This solution is from Chong Ching Tong, from River Valley High School, Singapore.

No, it is not possible.

When one oxygem atom splits it is destroyed and it forms one hydrogem and one nitrogem atom so the difference between the number of oxygem and the number of hydrogem atoms is increased by two. When a nitrogem atom splits it is destroyed and it increases the number of atoms of oxygem and of hydrogem both by one so the difference is the same. Then this continues for 1001 times and there will be 2002 more hydrogem atoms than oxygem atoms and no matter what we do we cannot lessen this number to 2001. The difference between the numbers of oxygem and hydrogem is never an odd number so it cannot be 2001.