Help!! Which of the following is a chemical reaction?

a. New atoms are formed when substances are mixed together
b. A solid material melts and becomes a liquid
c. Atoms of the reactants rearrange to form a new substance

Easy definition for atom and atomic mass

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

Ammonia and oxygen react to form nitrogen monoxide and water, like this: 4nh3 (g) + 5o2 (g) → 4no (g) + 6h2o (g) also, a chemist finds that at a certain temperature the equilibrium mixture of ammonia, oxygen, nitrogen monoxide, and water has the following composition: compound pressure at equilibrium nh3 65.1atm o2 31.3atm no 62.7atm h2o 65.8atm compound pressure at equilibrium nh3 65.3 atm o2 7.79 atm no 12.1 atm h2o 65.8 atm calculate the value of the equilibrium constant kp for this reaction. round your answer to 2 significant