I think the solution has something wrong
here my solution :
I convert everything to mole
Can you guys just check it
Because the Volumes of Pb(NO3)2 and NaI are equal, let them be 10(L)
then
* Before reaction :
moles of Pb(NO3)2 = 10*0.1 = 1(mole) => moles of Pb(2+) is 1 mole and NO3(-) is 2...