What primary standard acid can be used to standardise NaOH solutions by titration?
Oxalic acid dihydrate and KHP are the most comfortable acids for standardization, as their content per a unit of measurement (in this case it's obviously grams, as they are solid) hardly changes. When you have liquid acids, besides that what you've already mentioned, they can absorb water and other compounds from air. As they are liquid, people usually measure amount of those compounds by volume, and volume is a variable which depends on temperature, pressure.