Polymers

A cross-linked polymer is a type of polymer where the individual polymer chains are linked together by covalent bonds, forming a three-dimensional network. This cross-linking process significantly affects the properties of the polymer, making it more rigid, durable, and resistant to heat and chemicals.

Let's evaluate the given options:

Option A: Teflon

Teflon is a brand name for a polymer called polytetrafluoroethylene (PTFE). It is not a cross-linked polymer; rather, it consists of linear chains without cross-linking.

Option B: Polythene

Polythene or polyethylene is a polymer made from ethylene monomers. It can be either low-density polyethylene (LDPE), which has some branching, or high-density polyethylene (HDPE), which is mostly linear. Neither form is typically cross-linked.

Option C: Nylon

Nylon is a type of synthetic polymer, specifically a polyamide. Nylon polymers are generally linear and not cross-linked.

Option D: Bakelite

Bakelite is a type of phenol-formaldehyde resin, which is a thermosetting polymer. Thermosetting polymers are known for their heavily cross-linked structures. Bakelite forms an extensive, three-dimensional network through cross-linking, which makes it very hard and heat-resistant.

Therefore, the correct answer is:

Option D: Bakelite

The monomer units of nylon-6, 6 are hexamethylene diamine and adipic acid.

Starch is a polymer of glucose. In sucrose, two monosaccharide (glucose) units are joined by $\alpha$-1, 2 glycoside bond.