Which of the following chemical is present in an ant sting?

The acid present in an ant sting is methanoic acid.
Methanoic acid is also known as formic acid. The chemical formula is $\mathit{HCOOH}$. Methanoic acid is a weak acid that partially dissociates in an aqueous solution and occurs naturally in bee and ant stings. It is a corrosive acid and has toxic effects on the human body. It causes a burning sensation wherever the ant stings on the skin; The effect of methanoic acid can be neutralized by rubbing a mild base like baking soda solution on the stung area of the skin.