The correct answer is A. Formic acid.
Formic acid is a colorless, pungent-smelling liquid that is found in the venom of red ants. It is also found in some plants, such as stinging nettles. Formic acid is a weak acid, but it can cause a painful burning sensation when it comes into contact with skin or eyes.
Tannic acid is a yellow, astringent, water-soluble compound found in many plants, including oak bark, galls, and tea leaves. It is used in tanning leather and in some inks and dyes. Tannic acid is not found in red ants.
Oxalic acid is a colorless, odorless, crystalline solid that is found in many plants, including rhubarb, spinach, and sorrel. It is also found in some insects, such as fire ants. Oxalic acid is a strong acid that can cause severe burns when it comes into contact with skin or eyes.
Malic acid is a white, crystalline solid that is found in many fruits, such as apples, pears, and grapes. It is also found in some vegetables, such as tomatoes and potatoes. Malic acid is a weak acid that is used as a food additive and in some medicines.
In conclusion, the correct answer is A. Formic acid.