Final answer:
NaOH is the most basic compound among H2O, NaOH, HCl, and Na.
Step-by-step explanation:
The order of acidity or basicity can be determined by looking at the structure and properties of the compounds. In this case, we can compare the compounds based on their ability to donate or accept protons.
In the given options, NaOH is a strong base, HCl is a strong acid, and Na and H2O are neither acids nor bases. Therefore, between H2O, NaOH, HCl, and Na, NaOH is the most basic compound.