The three main types of scientific investigations are descriptive, comparative, and experimental. Which components are
included in all three types of investigations?
a scientific question
an independent variable
a dependent variable
a procedure
a control group
a conclusion

Can someone me with questions 12 and 13 plz.

What is the percent by mass of oxygen in fe2o3

The equation below shows a chemical reaction. a + b + heat —> c + d according to the law of conservation of energy, which statement is true? a. the reactants absorb heat because they have less energy than the products. b. the products release heat because they have more energy than the reactants. c. the reactants generate heat because they have more energy than the products. d. the products require heat to form because they have less energy than the reactants.