potassium react with chlorine to form potassium chloride
2K + Cl2 ---> 2 KCl
The reacting ratio of potassium reacted and KCl produced is 1:1
by use of this ratio the number of moles of KCl produced is therefore =6.78moles
mass =molar mass x number of moles
molar mass of KCl=74.5 g/moles
mass is therefore= 74.5 x 6.78moles=505.11g