A molecule M associates in a given solvent according to the equation M⇌(M)n.For a certain concentration of M, the van't Hoff factor was found to be 0.9 and the fraction of  associated molecules was 0.2. The value of n is

Let the degree of association be α                                               M⇌(M)n  Initially               1          0 After time         1-α     αnTotal moles after association =1-α+αn=1+1n-1α                        i=moles after association intial moles                                       =1+1n-1α1 or i-1=1n-1α                         .....(i) We have, i=0.9 and α=0.2On putting values of i and α in Eq. (i) we get n = 2