ok. (highlight to read)
Mr of Pb(NO3)2 = 331
=> mol of Pb(NO3)2 = Mass/Mr = 1/2
Mr of FeSO4 = 154
=> mol of FeSO4 was Mass/Mr = 1
Use the smaller no. of mol, so we're going to have 1/2 mol of produce.
Mr of product = 303
so mass = Mr x mol = 303 x 0.5
=151.5
which is 152 to 3sf, which we should convert to 150g (2sf), as we have all of our calculating values to 3 sf.