Which one of the following polymers is prepared by addition polymerisation ?

The correct option is Teflon.

Step-by-step Explanation:

To determine which polymer is prepared by addition polymerisation, let us look at the differences between the two main types of polymerisation:
1. Addition Polymerisation: This process involves the repeating linkage of monomer units containing unsaturated double or triple bonds. During this reaction, monomers join together to form a polymer without the loss or elimination of any small molecular side-products.
2. Condensation Polymerisation: This process involves the reaction between monomers containing two or more functional groups, resulting in the formation of a polymer along with the elimination of small molecules such as water, alcohol, or ammonia.

Now, let us analyze each of the options provided:

1. Teflon (Polytetrafluoroethylene or PTFE):
Teflon is prepared by heating its monomer, tetrafluoroethene, at high pressures in the presence of a free radical or persulphate catalyst. The reaction is represented as follows:

$n({\mathrm{CF}}_2={\mathrm{CF}}_2)\to {-[{\mathrm{CF}}_2-{\mathrm{CF}}_2]-}_n$

Since the unsaturated monomers simply add together without the elimination of any secondary molecules, Teflon is prepared by addition polymerisation.

2. Nylon-66:
Nylon-66 is a copolymer prepared by the condensation polymerisation of hexamethylenediamine and adipic acid, which proceeds with the elimination of water molecules.

3. Novolac:
Novolac is a phenol-formaldehyde polymer prepared by the condensation polymerisation of phenol and formaldehyde under acidic conditions, resulting in the elimination of water molecules.

4. Dacron (Terylene):
Dacron is a polyester prepared by the condensation polymerisation of ethylene glycol and terephthalic acid, accompanied by the elimination of water molecules.

Thus, only Teflon is prepared by addition polymerisation.