Final answer:
Suspensions require an auxiliary label stating "Shake well" because they are heterogeneous mixtures with particles that can settle, thus they must be well-shaken before administration to ensure even distribution.
Step-by-step explanation:
The liquid dosage forms that should have an auxiliary label stating "Shake well" are suspensions. Suspensions, like mud or milk of magnesia, are heterogeneous mixtures where the particles are suspended within the liquid and can settle to the bottom. This is why it is necessary to shake these medications before administration to ensure the particles are evenly dispersed throughout the liquid, providing the correct dosage when administered.