In Chinese, a syllable can be pronounced in one of four tones, the first tone, the second, the third tone, the fourth tone. Each tone stands for a different Chinese character. Since you haven’t given the accurate tone of these two syllables, I can only list the most frequently used characters for you.

ben: 
本(běn): a measure words for books, dictionaries, albums, ect. 
Eg. 一本书(yì běn shū) a book
fen: 
分(fēn): a measure word for Chinese currency RMB. One hundred fen is equal to one yuan

Hope  this helps you with your question.