The reaction of zinc with dilute and concentrated nitric acid, respectively, produces:

Zinc is a highly reactive metal (above hydrogen in the electrochemical series). When it reacts with dilute $$HNO_3$$, the acid is reduced to Nitrous oxide ($$N_2O$$), commonly known as laughing gas.

$$4Zn + 10HNO_3 (\text{dilute}) \longrightarrow 4Zn(NO_3)_2 + 5H_2O + N_2O \uparrow$$

With concentrated $$HNO_3$$, the oxidizing power of the acid is at its peak. Regardless of the metal's reactivity, concentrated nitric acid is predominantly reduced to Nitrogen dioxide ($$NO_2$$), which is characterized by its pungent-smelling brown fumes.

$$Zn + 4HNO_3 (\text{conc.}) \longrightarrow Zn(NO_3)_2 + 2H_2O + 2NO_2 \uparrow$$