In a ball-and-stick model of a molecule, different colored balls are used to represent different types of atoms. In the case of the model you described for a molecule of ethanol (C2H5OH), the components are as follows:
- Red ball: Typically represents oxygen atoms.
- Black balls: Typically represent carbon atoms.
- White balls: Typically represent hydrogen atoms.
- Sticks: Represent the bonds between the atoms.
Given that there are two black balls in the model, they represent the carbon atoms in the ethanol molecule.
So the answer is: carbon atoms.