What is the correct name for #C Cl_4#?
Covalent compounds use prefixes to identify the number of atoms of each element in the molecule.
In this case the first element is Carbon. There is one carbon atom which is the prefix mono = 1. However, we never use "mono" to begin the molecule.
The second element is Chlorine. IN this molecule there are 4 atoms of Chlorine which is the prefix tetra. The second element in the molecule always changes to the ending -ide.
Making the name Carbon TetraChloride.