Van't Hoff factor of 90% dissociated NaCl solution is

n=2 for

Mono basic acids….HCl, HNO₃, HCOOH, CH₃COOH  etc;

Mono acidic bases….MOH (M= monovalent cation), NH₄OH  etc;

Monovalent metal halides…..MX(NaX, KX etc) ;

Bivalent metal sulphates and carbonates…..MSO₄(MgSO₄, CaSO₄ etc), MCO₃(MgCO₃, CaCO₃ etc) ;

They all are classified as ‘AB’ type electrolytes…..$\mathrm{AB} \rightleftharpoons {\mathrm{A}}^{\mathrm{n}+}+{\mathrm{B}}^{\mathrm{n}-} ;$ n=2

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

when n= 2 …Van't Hoff factor, i = $1+\mathrm{\alpha }$ ; 

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

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

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

$\mathrm{\alpha }$ for x% ‘AB’ = $\frac{\mathrm{x}}{100}$;