All three of these acid names are old, common names that literally describe where the acid was first isolated from, so the fastest way to match them is to remember the everyday source rather than the structure.
Formic acid gets its name from the Latin word formica, meaning ant, because it is the irritant injected in ant and bee stings, so it pairs with ant.
Acetic acid is the sour, active ingredient of common vinegar, formed by oxidising ethanol, so it pairs with vinegar.
Butyric acid is the compound responsible for the sharp, unpleasant smell of rancid butter, its very name comes from the Greek word for butter, so it pairs with butter.
Putting these together, formic acid with ant, acetic acid with vinegar, and butyric acid with butter, which in the List-I and List-II labelling reads a-(iii), b-(i), c-(ii).
