Hydrogen fluoride is a liquid at room temperature due to =>>>
(i) dimerisation
(ii) dissociation followed by aggregation
(iii) association
(iv) polymerisation

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Please find below the solution to the asked query:
Hydrogen flouride is liquid at room temperature due to association.
Hence option (iii) is the correct answer.
Though HF is a diatomic molecule, it forms very strong intermolecular hydrogen bonds  and thus at room tempertaure it forms a zig-zag chain of molecule by association as shown below:
                            

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