If I want to focus on 2 keywords: "mass" and "bulk", will using word "mass/bulk" as a main keyword works? Or I should split the word into "mass bulk"? Any suggestions?
if this is 2 keywords then use like this "Mass - Bulk" through hyphen google count them different keywords.
There is no problem using '/'. In fact, it's proper English to use '/' to separate two words that mean the same thing in a sentence. Google will see '/' just as they would '-' or '|'. They all get treated as a space when they are evaluated for keywords.