How can we determine which compound was present in a container labelled KNO3 or K2CO3 or KNO2?

The reaction of K₂CO₃ will vinegar solution, evolves carbon dioxide gas.

But the other two compounds KNO₃ and KNO₂ does not evolve carbon dioxide on reaction with vinegar.

The reaction of KNO₂ with sulfuric acid gives, a brown gas, of nitrogen dioxide.

And the rest two compounds, K₂CO₃ and KNO₃, does not react with sulfuric acid.