Answer:
Formulae: mass = number of moles × Mr or Ar
The substance may be a compound or an element
so if it is a compound, find its Mr
it is an element find its Ar in the periodic table
the original formula is that:
number of moles = mass ÷ Mr or Ar
so if they ask for mass, make make mass the subject of formula
if they ask for number of moles, make number of moles the subject of formula
then replace the value......
