Which of the following natural sources contains methanoic acid?

The correct answer is Option (2) → Nettle sting

Methanoic acid (formic acid, HCOOH) is the acid injected by the stinging hairs of the nettle leaf and by the sting of an ant, which is why the sting burns. Rubbing the spot with the leaf of the dock plant, which grows near the nettle, gives relief, since the dock leaf is basic and neutralises the acid.