4bii) first understand the q.
FeCl3 + 3NaOH --> Fe(OH)3 + 3NaCl
moles of FeCl3 = conc. * volume = 1 * 4/1000 = 0.004
MOles of NaOH = 0.004*3 = 0.012 or conc. * volume = 1 * 12/1000 (look at graph) = 0.012
when FeCl2 is used, this is the equation
FeCl2 + 2NaOH --> Fe(OH)2 + 2NaCl
Moles of FeCl2 = conc. * volume = 0.004
but here, the mole ratio is 1:2
so the moles of NaOH = 0.004 * 2 = 0.008
volume = moles/conc. = 0.008/1 = 0.008dm^3 = 8cm^3
thus, for FeCl2 --> 8cm^3 of NaOH reacts completely with FeCl2, so, the shape wud be same, only it wud become constant (parallel to x-axis) at 8cm^3 of NaOH