# The number average molecular mass and mass average molecular mass of a polymer are respectively 30,000 and 40,000. The poly dispersity index of the polymer is

$\begin {array} {1 1} (a)\;< 1 & \quad (b)\;> 1 \\ (c)\;1 & \quad (d)\;0 \end {array}$

The dispersity from polymerization is often denoted as $D =\large\frac{M_w}{M_n}$ , where $M_w$ is the weight average molecular weight and $M_n$ is the number average molecular weight. $M_n$ is more sensitive to molecules of low molecular mass, while $M_w$ is more sensitive to molecules of high molecular mass
Here $D=\large\frac{40,000}{30,000}$which is $>1$
Ans : (b)
answered Mar 12, 2014