Which of the following statements about polymers is correct?
(1) The ratio of the weight average and number average molecular masses,
\(\bar{M}_{\text {. }} / \bar{M}_{n}\), is called poly dispersion index (P.D.I.)
(2) The number average molecular mass, \(\overline{\mathrm{M}} \mathrm{n}\) and
the weight average molecular mass \(\bar{M}_{w}\) are expressed by the equations
\(\overline{\mathrm{M}}_{\mathrm{w}}=\frac{\sum \mathrm{N}_{\mathrm{i}}
\mathrm{M}_{\mathrm{i}}}{\sum \mathrm{N}_{\mathrm{i}}
\mathrm{M}_{\mathrm{i}}}\) and \(\overline{\mathrm{M}}_{\mathrm{w}}=\frac{\sum
\mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}^{2}}{\sum
\mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}}\)
Here, \(\mathrm{N}_{i}\) is the number of molecules of molecular mass
\(\mathrm{M}_{i}\) of the species \(\mathrm{i}\).
(3) Some physical properties such as freezing point, vapour pressure and
osmotic pressure are related directly to \(\mathrm{M}\) whereas some other
physical properties like light scattering, sedimentation and diffusion
constant are related directly to \(\mathrm{M}_{w}\).
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) 1,2 and 3
