1) In the reaction 2H2 + O2 → __H2O, what coefficient should be placed in front of H2O to balance the reaction? a) 1
b) 2
c) 3
d) 4

2) In the reaction 4Al+3O2→_Al2O3, what coefficient should be placed in front of the Al2 to balance the reaction?
a) 1
b) 2
c) 3
d) 4

3) How does the law of conservation of mass apply to this reaction: C2H4 + O2 → H2O + CO2?
a) The equation needs to be balanced. There are fewer oxygen atoms in the equation than hydrogen or carbon.
b) Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.
c) The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation.
d) Each element needs to be balanced.

4)How does the law of conservation of mass apply to this reaction: Al + 3HCl → H2 + AlCl3?
a) Only the hydrogen needs to be balanced. There are equal numbers of aluminum and chlorine.
b) The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation.
c) Hydrogen and chlorine need to be balanced. There is an equal amount of aluminum on each side.
d) The equation needs to be balanced. There are fewer hydrogen atoms in the equation than aluminum or chlorine.