What is the name for #C Cl_4#?
Since this is a covalent compound, not an ionic compound, don't make the mistake of saying it is carbon chloride.
Refer to a list of prefixes, I'm pretty sure it goes like:
Dont write Mono in front of the first compound, you can omit it, but you have to write it for the second part of the compound if its only 1. In this case, theres 1 carbon and 4 chlorine, hence, carbon tetra-chloride.