Which of the following statement about polymers in correct?

Options

A. The number - average molecular `overline(M_(n))` and the weight - average molecular mass, `overline(M_(w))` are expressed by the equations
`overline(M_(n)) = (sum N_(i) M_(i))/(sum N_(i))` and `overline(M_(w)) = (sum N_(i) M_(i)^(2))/(sum N_(i) M_(i))`
where `N_(i)` is the number of molecular mass `M_(i)` of the species `i`.
B. Some physical properties such as freezing point, vapor pressure and osmoric pressure are related directly to `overline(M_(n))` whereas some other physical properties lie light - scattering, sedimantation and difusion constant are related direclty to `overline(M_(w))`
C. The ration of the weight - average and number - average molecular masses, `overline(M_(w))//overline(M_(n))` is called poly dispersity index `(PDI)`,
D. All of these

Answer

D

Explanation

`overline(M_(n)) = (sum N_(i) M_(i))/(sum N_(i))`
`overline(M_(w)) = (sum N_(i) N_(i)^(2))/(sum N_(i) N_(i))`
`PDI = (overline (M_(w)))/(overline(M_(n)))`