The reaction is a decomposition…
[tex]2KNO_3 \longrightarrow 2KNO_2 + O_2\\[/tex]
… because one substance is forming two other substances.
[tex]\text{2K}\stackrel{\hbox{+5}}{\hbox{N}} \stackrel{\hbox{-2}}{\hbox{ O}}_3 \longrightarrow \text{2K}\stackrel{\hbox{+3}}{\hbox{N}}\text{O}_2 + \stackrel{\hbox{0}}{\hbox{O}}_2\\[/tex]
It is also a reduction-oxidation reaction because the oxidation number of N decreases from +5 to +3 and the oxidation number of O increases from -2 to 0.
