1. O2 is not a compound because it only contains one or more type of the same element atom.
2. O2 is a molecule because a molecule is one or more of the same element atom.
3. The law of conversion is that the mass of the system will stay the same when transfer takes place. Like if you had an equation O+H2—> H2O the mass will remain the same.
4. It will be equal to 10 because of law of conservation of matter.
5. One observation can be that the compound, reaction you’re observing, has change states.
The first answer is -.595454 the second answer is -1.9488
If you want an example then a car passing by a standing man is the best one !!
You can see a physical change always but not always a chemical
