Polyamide linkage is present in

Choose the correct option$(s)$ from the following:
$(1)$ Natural rubber is polyisoprene containing trans alkene units.
$(2)$ Nylon-$6$ has amide linkages.
$(3)$ Cellulose has only $\alpha-D$-glucose units that are joined by glycosidic linkages.
$(4)$ Teflon is prepared by heating tetrafluoroethene in the presence of a persulphate catalyst at high pressure.

Select the incorrect option for the following polymer:

Which of the following is a polymer containing nitrogen?

The turbidity of a polymer solution is a measure of ........

Low density polythene and high density polythene,both are polymers of ethene but there is marked difference in their properties. Explain.