How many moles of pb are required if 8 moles of pbcl2 are produced

8 moles

Justification:

1) The law of conservation of mass lets you to conclude that the amount of Pb in the reactants is the same amount of Pb in PbCl₂.

2) That is the great use of the chemical formulas of the compounds, they tell you the number of atoms (or moles of atoms) per molecules of compounds (or mole of molecules).
3) Then, as the chemical formula indicates that every molecule of PbCl₂ has 1 atom of Pb, you directly can conclude that 8 moles of PbCl₂ require 8 moles of Pb.