Which formula is used to represent the three-dimensional structures of molecules using a two-dimensional surface like a sheet of paper or a computer screen?

Dash-wedge formula

The correct answer is option 3. Dash-wedge formula.

The formula used to represent three-dimensional structures of molecules using a two-dimensional surface like a sheet of paper or a computer screen is the "dash-wedge formula" or "wedge-dash formula." This notation is used to indicate the spatial arrangement of atoms and groups around a central atom in a molecule. The lines and wedges represent bonds coming out of the plane of the paper (wedges) or going into the plane of the paper (dashes), providing a more accurate representation of the molecular geometry.