The reversible reaction, 2NO{g) ⇌ N2 (g) + O2 (g), would be classified as a reaction. homogeneous
heterogeneous
endothermic

smooth muscle is composed of involuntary muscles found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. those muscles push materials like food or blood through organs. unlike skeletal muscle, smooth muscle can never be under your control.