Here's why:

* Atoms: Seawater is primarily composed of water (H₂O), which is a molecule made up of hydrogen (H) and oxygen (O) atoms. Additionally, seawater contains dissolved salts, which are composed of various atoms like sodium (Na), chlorine (Cl), magnesium (Mg), potassium (K), and others.

* Molecules: Seawater contains numerous molecules, including:

* Water molecules (H₂O)

* Salt molecules (NaCl, MgCl₂, KBr, etc.)

* Dissolved gases (oxygen, nitrogen, carbon dioxide)

* Organic molecules (from marine life and decomposition)

So, seawater is a complex mixture containing both individual atoms and various types of molecules.