Question 1 in the reaction c7h16 + o2 → 8h2o + 7co2, what coefficient should be placed in front of o2 to balance the reaction? a. 7 b. 8 c. 11 d. no coefficient is needed question 2 in the reaction h2 + o2 → 2h2o, what coefficient should be placed in front of h2 to balance the reaction? a. 1 b. 2 c. 3 d. no coefficient is needed question 3 how does the law of conservation of mass apply to this reaction: c2h4 + 3o2 → 2h2o + 2co2? 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. question 4 how does the law of conservation of mass apply to this reaction: mg + hci → h2 + mgci2? a. the equation needs to be balanced. there are fewer hydrogen atoms in the equation than magnesium or chlorine. b. only the hydrogen needs to be balanced. there are equal numbers of magnesium and chlorine. 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. hydrogen and chlorine need to be balanced. there is an equal amount of magnesium on each side.