Which acid is the best choice to create a buffer with ph= 3.19?

The best choice is hypochlorous acid nitrous acid (HNO2) because it has the nearest value of pK to the desired pH.
pKa of nitrous acid is 3.34 
If we know pKa and pH values,  we can calculate the required ratio of conjugate base (NO2⁻) to acid (HNO2) from the following equation:
pH=pKa + log(conc. of base)/( conc. of acid)
3.19=3.34 + log c(NO2⁻)/c(HNO2)
3.19 - 3.34 = log c(NO2⁻)/c(HNO2)
-0.15 = log c(NO2⁻)/c(HNO2)
c(NO2⁻)/c(HNO2) = 10⁰¹⁵ = 1.41

False, as a substance changes from a solid to a liquid and from a liquid to a gas the molecules get farther apart from each other