* Organic molecules are defined as molecules containing carbon (C) and hydrogen (H) atoms, and often other elements like oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P). They are the building blocks of life and form the basis of biochemistry.

Let's break down the other molecules:

* H2O (water): This is inorganic. It contains hydrogen and oxygen, but not carbon.

* NaCl (sodium chloride, table salt): This is inorganic. It contains sodium and chlorine, but not carbon or hydrogen.

* NaOH (sodium hydroxide, lye): This is inorganic. It contains sodium, oxygen, and hydrogen, but not carbon.

Therefore, CH4 is the only organic molecule in the list.