The correct answer is option 2: 2 and 4 only.

Vitamins are essential nutrients that our body needs to function properly. They are organic compounds that our body cannot produce in sufficient quantities, so we need to obtain them through our diet.

Looking at the options:

1. Acetic acid is a weak acid and does not possess any vitamin properties. It is mainly used as a preservative in food.

2. Ascorbic acid, also known as vitamin C, is a well-known vitamin that plays a crucial role in maintaining our immune system, promoting collagen production, and acting as an antioxidant.

3. Citric acid is a weak acid and does not possess any vitamin properties. It is commonly found in citrus fruits like lemons and oranges and is often used as a preservative or flavoring agent in foods.

4. Folic acid is a synthetic form of folate, which is a B-vitamin. It is important for DNA synthesis and cell division, making it especially important for pregnant women to prevent birth defects.

Therefore, only ascorbic acid (vitamin C) and folic acid are vitamins, so the correct answer is option 2: 2 and 4 only.