What type of reagent is required to convert NO2 - to HNO2?  base  oxidizing agent  acid  reducing agent  precipitating agent
The oxidation state of N is same in both
"NO_2^-" and "HNO_2"
so there is no oxidation or reduction reaction.
this is a simple acid base reaction :
so it require an Acid.
it reacts in a reversible reaction.
"HNO_2 +H_2O \\rightleftharpoons NO_2^- +H^+"
which can be also,
"NO_2^- +H^+\\rightleftharpoons HNO_2 +H_2O"