Van't Hoff factor of 15% dissociated Potassium phosphate solution is

They all are classified as ‘A₃B’ type(uni-trivalent) electrolytes…..${\mathrm{A}}_3\mathrm{B} \rightleftharpoons 3{\mathrm{A}}^{+}+{\mathrm{B}}^{3-} ;$ n=4

Examples….M₃PO₄

                     Van't Hoff factor, i = $1-\mathrm{\alpha }+\mathrm{n\alpha }$ ;

    when n= 4

                    Van't Hoff factor, i = $1+3\mathrm{\alpha }$ ; 

n=4….for AB₃ type(tri-univalent) electrolytes…...${\mathrm{AB}}_3 \rightleftharpoons {\mathrm{A}}^{3+}+3{\mathrm{B}}^{-} ;$ n=4

Examples…..AlF₃, Al(NO₃)₃

$\mathrm{\alpha }$= Degree of ionization  (or) dissociation ;

Ex ; For 5% ionized electrolyte  $\mathrm{\alpha }=\frac{5}{100}= 0.05 ;$

0.1, 0.15, 0.2, 0.25, 0.3…..for 10%, 15%, 20%, 25%, 30% ionized electrolyte

$\mathrm{\alpha }$ for x% electrolyte = $\frac{\mathrm{x}}{100}$; 

For AB₃ or A₃B type : i= 1+3$\mathrm{\alpha }$ ;

i= a) 1.15….5% ionized  b) i= 1.3…..10% ionized c) i=1.45….15% ionized d) i= 1.6…..20% ionized…..

Hint: For every 5% increase in ionization i.e for every 0.05 units increase in $\text{'}\mathrm{\alpha }\text{'}$ value ‘i’ increases by 0.15 units ;