Question: why hno2 is a weak acid?
Answer: Most mineral acids like HCl, H2SO4 and HClO4 are fully dissociated in solution, and pH of their 0.1N solutions are all much less than 1.0. ... So, HNO2 exists in solution at an equilibrium between undissociated HNO2 and H+ and NO2- ions, at a 0.1N concentration. Therefore, it is clear that HNO2 is a WEAK ACID.