• question_answer A molecule M associates in given solvent according to the equation $\operatorname{M}\underset{{}}{\overset{{}}{\longleftrightarrow}}{{(\operatorname{M})}_{\operatorname{n}.}}$ For a certain concentration of  M, The van? t Hoff factor was found to 0.9 and the fraction of associated molecules was 0.2 The value of n is:     JEE Main  Online Paper (Held On 22 April 2013) A)  3                                            B)  5C)  2                                            D)  4

van't Hoff factor (i) and the degree of association are related as below: $i=1-\alpha \left( 1-\frac{1}{n} \right)$ $0.9=1-0.2\left( 1-\frac{1}{n} \right)$ On solving, $\left( 1-\frac{1}{n} \right)=\frac{1}{2}$ $\frac{1}{n}=1-\frac{1}{2}=\frac{1}{2}$ $\therefore$ $n=2$