Answer: [tex]Na_3PO_4[/tex]
Explanation:
Depression in freezing point is given by:
[tex]\Delta T_f=i\times K_f\times m[/tex]
[tex]\Delta T_f[/tex] = Depression in freezing point
i= vant hoff factor
[tex]K_f[/tex] = freezing point constant
m= molality =[tex]\frac{moles}{\text {weight of solvent in kg}}=\frac{1}{1}=1m[/tex]
1. For [tex]PbS[/tex]
, i= 1 as it is a non electrolyte and does not dissociate.
2. For [tex]C_8H_{18}[/tex]
, i= 1 as it is a non electrolyte and does not dissociate.
3. For [tex]Na_3PO_4[/tex]
, i= 4 as it is a electrolyte and dissociate to give 4 ions.
[tex]Na_3PO_4\rightarrow 3Na^{+}PO_4^{3-}[/tex]
4. For [tex]NaCl[/tex]
, i= 2 as it is a electrolyte and dissociate to give 2 ions.
[tex]NaCl\rightarrow Na^{+}+Cl^{-}[/tex]
Thus as vant hoff factor is highest for [tex]Na_3PO_4[/tex] and the freezing point will be most affected.
