INSOUCIANT : GOSSAMER

'Insouciant' refers to someone showing a lack of concern, and 'Gossamer' refers to a fine, filmy substance consisting of cobwebs spun by small spiders, seen especially in autumn.

'Nymph' is a mythological spirit of nature imagined as a beautiful maiden inhabiting rivers, woods, or other locations, while 'Gehenna' is a place or state of misery.

Since this word pair does not share any relationship with the input pair, the correct option is A.