Answer:
Hydrochloric acid (HCL) is an acid, while sodium hydroxide (NaOH) is a base.
In this case the two labels are missing, one method to differentiate them is by mixing each reagent with a base. Let's say we mix sodium carbonate(Na2C03) which is a base with each of the reagent, the sodium carbonate will likely react with Hydrochloric acid which is an acid to form NaCl and H2O, but it will not react with sodium hydroxide which is a base.
Therefore, by mixing the each reagent with a base, we could help place the correct label.
Another way to place the labels correctly is, the bottle containing hydrochloric acid will be sticky while the sodium hydroxide will be slippery. It is a known fact that acids are generally sticky while bases are slippery when touched.
