How many moles does 270g kbr have?

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

Choose an equation that represents an enzyme-catalyzed reaction. (a) enzyme + substrate → enzyme-substrate complex (b) enzyme + substrate ←−→ enzyme + products (c) enzyme + substrate ←−→ enzyme-substrate complex → enzyme + products (d) enzyme + substrate ←−→ enzyme-substrate complex → enzyme-substrate complex + products

Measurements that have similar values are: a. usually accurate b. sometimes accurate c. always accurate d. never accurate