Why $$HF$$ forms $$H-$$bonding with ethyne even through it is non-polar in nature?
Due to $$sp$$ hybridization of carbon, the electrons of the $$C-H$$ bond of ethyne are attracted towards carbon. As a result, carbon carries a partial negative charge while $$H$$ carries a partial positive charge. Because of the presence of partial positive charge on $$H$$, ethyne forms $$H-$$ bond with the $$F-$$atom of the $$HF$$ molecules as shown below:
$$H-C\equiv \overset{\delta -}{C}-\overset{\delta +}{H} -------\overset{\delta -}{F}-\overset{\delta +}{H}$$