Hi!!!
Hope you are doing well.
100 atoms of A+ 100 molecules of B means 100 atoms of A will react with 100 molecules of B. Thus, both the reagents are present in stoichiometric amounts.
Hope you are clear now. Feel free to ask if you have any other queries. All The Best!!!
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile