Answer:
The circular path and electron revolves around the nucleus in an atom is called shell or orbit.
You don't have to worry about converting to moles and back to liters. You need to know about Gay-Lussac's law of combining volumes. Coupled with Avogadro's law which says that the moles of gas are proportional to the volume, all we have to do is:
2H2(g) + O2(g) -> 2H2O(g)
2L ..........1L ..........2L
7.25L .....3.63L .....7.25L
The only work is dividing 7.25 by 2.
The one with the lower atomic/molecular mass
3 Mg + 1 Fe2O3 →2 Fe + 3MgO
Type of Reaction: Single displacement.