Multiple choice chemistry quiz​

How are isotopes of the same chemical element alike? how are they different?

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Which change will decrease the number of effective collisions during a chemical reaction? a. adding a catalyst b. increasing the surface area c. decreasing the temperature d. increasing the reactant concentrations e. increasing the volume of the reactants