J.R. S. answered 04/22/20
Ph.D. University Professor with 10+ years Tutoring Experience
2NH4I(aq) + Pb(NO3)2(aq) ==> 2NH4NO3(aq) + PbI2(s) ... balanced equation
moles Pb(NO3)2 present = 0.853 L x 0.440 mol/L = 0.3753 moles
moles NH4I needed to react = 0.3753 mol Pb(NO3)2 x 2 mol NH4I/mol Pb(NO3)2 = 0.751 moles NH4I
Volume NH4I: (x L)(0.170 mol/L) = 0.751 moles
x = 4.42 L of NH4I needed