What is formula mass?

How many moles of al3+ ions are in 1.25 moles of al2o3

Ammonium perchlorate nh4clo4 is the solid rocket fuel used by the u.s. space shuttle. it reacts with itself to produce nitrogen gas n2 , chlorine gas cl2 , oxygen gas o2 , water h2o , and a great deal of energy. what mass of nitrogen gas is produced by the reaction of 2.1g of ammonium perchlorate?

If e is the symbol for an element, which two of the following symbols represent isotopes of the same element? 1. e2. e3. ea.1 and 2c.1 and 4b.3 and 4d.2 and 3