Which of these must be the same on both sides of a balanced chemical equation?

A the number of atoms
B the number of compounds
C the number of molecules
D the number of solids, liquids, and gases

Iam in desperate need of with this !

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?

Marcel just purchased 1.69 grams of iron fillings in order to make living putty for his 6 year old niece. how many moles of iron are made in his sample?