Which solution is a buffer? • 0.100 m hno2 and 0.100 m hcl • 0.100 m hno3 and 0.100 m nano3 • 0.100 m hno2 and 0.100 m nacl • 0.100 m hno2 and 0.100 m nano2?

A buffer has roughly equal concentrations of a weak acid and its conjugate base. The only acids in the question are HNO3 and HNO2. HNO3 is a strong acid, so it can’t be used for a buffer. The first option has HNO2 and hydrochloric acid, which won’t supply the conjugate base of HNO2, which is NO2^-1. NaCl isn’t an acid or a base, so we can eliminate that as well. That leaves us with HNO2 and NaNO2. Group 1 metals are spectators in acid-base equilibria, so we can ignore Na once it disassociates. That will give us .1M HNO2 and .1M NO2^-1, which is what we want.