If you wanted to be certain that someone knew exactly what substance you meant ? would you give CAS number? ?

Question

would you give the CAS number or one of the other names of the chemical or substance?

Answer 1

Yes, you should give the CAS number. Systematic IUPAC names are acceptable also.

Edit: There are advantages and disadvantages of each. CAS numbers can be readily looked up, but need to be registered, and a newly synthesized compound will not be in the CAS registry. The IUPAC name can be used in such a case, but it can be complex and difficult to understand.